Kit Building – AB1DQ

Bayou Jumper in a Cigar Box

I was thrilled to see that the good folks at the Four State QRP Group released the 4th revision of their popular Bayou Jumper 40M CW Transceiver designed by Jim Giammanco N51B and David Cripe NM0S last year.

The Bayou Jumper, first released in 2017, is a 40M QRP transceiver that is an homage to the classic Paraset, the legendary transmitter/receiver supplied to the resistance groups in France, Belgium and the Netherlands during World War II.

Whaddon Mk VII – Paraset Clandestine Transceiver c. 1942

The Bayou Jumper, an updated solid state CW only radio kit is intended to be fitted into a hinged wooden suitcase style box available from Hobby Lobby or any other similarly sized box.

Given my recent obsession with building QRP radios and accessories into empty cigar boxes, I felt the Bayou Jumper would make an excellent candidate for cigar box treatment. I found a gorgeous Perdomo 20th Anniversary cigar box in my stash that was approximately the right size, featured gorgeous red and gold artwork on a black background and was constructed of heavier wood than many of the other cigar boxes in my collection.

The Bayou Jumper front panel was a perfect flush fit left to right in the Perdomo box, and only fell 1/2″ short front to back. I modified the box by gluing a 1/2″ square dowel along the top hinged edge to fill the empty space.

Other mods I made to the cigar box included:

Adding weights to the bottom of the box to prevent the radio from tipping over backward when the lid was up and to provide a little more heft,
- Adding a pair of latches to be able to secure the lid closed, and,
  - Reinforcing the original pressed in hinges with three supplemental screw-in hinges.

Building the Kit

I chose the Bayou Jumper to be my 2022 Christmas project. Professionally I have worked in an administrative role in higher ed for the past two decades and one of the biggest perks of working at most leading universities is they completely shut down for an extended winter recess. Building an electronic kit during my winter recess takes me back to my teenage years when I’d spend my holiday break from school constructing the electronic kits I received as Christmas gifts.

Like every NM05 designed 4SQRP kit I have previously built (the Murania One Transistors Boy’s Radio, the 4S-QRP Antenna Tuner, and the Ozark Patrol Regen Shortwave Receiver), assembly was a relaxing no-stress experience. Once again, I was very pleased with the high quality of the double sided etched-through printed circuit board, the quality of the electronic components and hardware, and the in-depth and easy-to-understand instructions and documentation.

I encountered only two minor issues in building the Bayou Jumper Revision D that were hardly a problem, barely an inconvenience.

The first was a missing resistor, R15, a 1/4 watt 100K ohm resistor. I have never experienced a missing part when building a 4SQRP kit and it’s probably just as likely I dropped or lost the resistor than it was wasn’t shipped in the kit. Regardless, I had the correct value resistor on hand in my home stock supply.

The second matter involved the jumper wires provided to supply current to the multi-color LED on the front panel from the main PCB. The instructions stated the kit included a 12″ jumper wire with header pins included in the kit that needed to be cut in half to make two jumpers. However, the jumper wire included in my kit was only 5.5″ long and once cut it in half as the instructions directed, one of the resulting leads was too short to mate to the header pin on the PCB.

As with the missing resistor, I had plenty of jumper wires that I use for breadboard prototyping on hand and was able to create the necessary jumper wires with sufficient slack to reach the contact points.

All in all, the kit went together in just 3 days’ time as I prefer to work slowly and methodically whenever I build a kit. (Whenever I rush through a project I typically find that any time I saved working quickly would be lost in extensive time consuming trouble-shooting that would be needed!)

The topside of my populated PCB. Assembling the kit was straightforward and fun.

Winding the Transformer

The Bayou Jumper features three inductors etched into the PCB but still requires the winding of a single transformer on a T 6-7 toroid core. I have never found winding coils to be difficult or stressful, and in fact, I generally enjoy it especially when the kitter provides excellent directions and illustrations, which 4SQRP did.

The transformer required 3 windings, one of 19 turns, one of 4, and the last of 2. The completed transformer can be soldered to either the top or bottom side of the PCB, based on the builder’s preference and tje screen printing on the circuit board makes installing the completed transformer essentially foolproof. I chose to mount the transformer to the bottom side of the board to make it easily accessible for adjusting the spacing of the winding to adjust the receiver’s tuning range.

The completed transformer mounted to the bottom side of the PCB.

Faux Crystals?

The Bayou Jumper’s crystal socket accepts the classic FT-243 crystal form, a popular Cold War era crystal size that today is no longer manufactured and increasingly rare.

The Bayou Jumper comes supplied with a pair of HC-49 crystals for 7.030 and 7.122 MHz, and two crystal adapter boards to fit the HC-49 crystals into the FT-243 sockets.

Vintage FT-243 cases are large enough to accommodate modern small HC-49 crystals and with its 3 screws, the FT-243 can be easily opened and re-sealed, making it possible to re-stuff FT-243 cases for modern QRP use.

Using several of the FT-243 crystals for non-amateur frequencies that I picked up at ham-fests, I have modified 9 crystals for use on the 40 meter CW sub band, all ready to go in my Bayou Jumper.

Receiver Alignment and Final Assembly

Again, the excellent directions made aligning the receiver a snap. Instructions are provided for a variety of alignment methods using an oscilloscope, a frequency generator or a calibrated receiver capable of CW reception. Having all three available to me, I tried all three methods and was pleased when all three were in sync.

I started taking a frequency reading with the tuning dial set to the low end of the scale with my O-scope and read 6.897 MHz.

Next I tried sweeping the dial of my frequency counter to spot the point where oscillation could be heard in the earphones. My frequency counter has an analogue scale and was able to read the resonant frequency at about 6.9 MHz.

Finally I set my portable C. Crane Skywave SSB travel radio for LSB and tuned to the 6.900 and tuning up and down was able to hear the receiver’s oscillator at about 6.895 MHz.

Following the directions to adjust the tuning range by spacing the L1 windings on the transformer closer together or further apart and then adjusting the C30 trimmer, I was able to achieve a final tuning range of 7.000 – 7.167 MHz which should be more than adequate for the CW sub-band I would use.

Finally, I followed the directions to verify regeneration and was happy to find that my receiver needed no further adjustment. Satisfied with my work, I mounted the radio in the cigar box and am looking forward to putting my Bayou Jumper on the air.

Stay tuned for Part II where I will report on my experience operating the Bayou Jumper on the air and any future adjustments or modifications.

Elecraft K2 Build – Part 2

Front Panel Assembly

March 20, 2022

This morning I completed the Front Panel Board, the second board of the Elecraft K2 HF Transceiver Kit build that I began at the start of the year. After completing the Control Board on January 17, I took a complete month off working on other weekend projects before starting the Front Panel on February 21. I did state from the get go that I was going to take my time with this, my most ambitious kit build, and I’m staying true to my word.

The Front Panel Board is where all of the user controls are mounted. These include the large rotary encoder/tuning knob, the numeric keypad and pushbuttons, and five variable resistors. This section also includes the graphical LED status bar display and the LCD main display.

Assembly of the front panel starts by soldering the sixteen tactile push button switches to the printed circuit board. For a proper and neat professional appearance, it’s essential that all of the switches be mounted at a precise uniform distance from the surface of the board.

Elecraft provides a nifty switch spacing tool in the kit which is essentially a thin narrow bit of PCB material that is placed under each switch which is then pushed flush to the spacing tool. This clever method worked exceptionally well for me.

After the switches are mounted, the board is populated with the usual components – resistors, capacitors, diodes and transistors. The front panel board has four ICs including the large 40 pin U1 which is mounted on the bottom side of the board and behind the display.

The front panel board also has a good bit of hardware to be attached including the eight-pin microphone jack and several spacers. Up to this point the instruction manual has been absolutely excellent in providing detailed easy to follow accurate directions.

However, I did encounter some difficulty when it came to mounting the main display components which consists of two backlight LEDs, their spacers, a white cardboard reflector, a frosted plastic diffuser, and the 40 pin LCD.

As I discussed in my previous post, the Elecraft K2 is a fabulous kit, but it’s a rather old kit, first prototyped a quarter century ago – in 1997! Understandably in the time since its introduction, some components become ‘unobtainium’ as the years go by. Vendors come and go and with advancing technology, manufacturers discontinue production of now archaic through-hole components with today’s increasing popularity of SMD architecture.

Thus, when one buys a K2 kit today, it will come with several pages of errata that must be carefully consulted and reviewed. Builders in 2022 will find themselves crossing out sections, sometimes whole pages, of the original manual, and adding notes about the replacement modern components packaged with their kit.

This was the case with the display assembly. I was instructed to cross out most of the directions pertaining to the installation of the display on pages 27 and 28 of the manual and to follow the alternative directions provided as errata.

The revised directions call for the builder to first insert the leads of a pair of rectangular LEDs through plastic spacers and solder the LEDs flush to the board to the left and the right side of where the LCD will be mounted.

Between the two LEDs, the builder places a white cardboard backlight reflector and then mounts a frosted plastic diffuser by placing it over the the two LEDs on the left and the right side. The diffuser has an indent on each side to accomondate the LEDs.

I found this all went precisely as described until I came to the step that instructed me to place the LCD flush on top of the diffuser and then solder the 20 pins of the LCD to the associated pads on the PCB.

None of the LCD pins were long enough to go through the holes in the pads on the board. If pressed flush to the diffuser the LCD pins just barely touched the pads.

With the LCD flush against the frosted crystal diffuser, the pins are too short to penetrate the holes in the pads.

A view of the bottom side of the board showing the inadequate length of the LCD pins.

I carefully checked the instructions and my work. I was certain I mounted the LEDs correctly and flush to the board with their spacers, and the cut outs on the bottom side of the plastic diffuser neatly accommodated the LEDs perfectly.

Realizing that proper positioning of the LCD would be critical for the PCB to properly fit in the front panel and knowing that not getting the spacing correct would also give the finished radio a sloppy appearance, I reached out to Elecraft for help via their website.

I dreaded the prospect of having to de-solder 20 pins and run the risk of damaging the LCD if I needed to remove it after it was soldered in place. I wanted to get as much information as I could before proceeding.

I received an email reply from Dave at Elecraft who is their K2 support guy within a couple of days. Dave stated that it was ‘perfectly normal’ for the LCD pins to just touch the top pads on the PCB and that they do not need to protrude through the holes. He said that his last K2 build was like this and suggested that I carefully solder the 20 pins from the topside, but to make sure the LCD is level and parallel to the board.

I did as Dave recommended, carefully aligning the LCD so it was level and evenly spaced above the board. I started by soldering each of the corner pins and confirming the LCDs position after each solder joint. Once done, I applied solder to the pads on the bottom of the board to let it flow through the hole to help ensure solid contact.

However, after I soldered just under half of the LCD pins, I realized I had left out the cardboard reflector. D’oh! There was no way I could slide the stiff cardboard under the pins at this point and I didn’t want to have to de-solder so many pins, so I came up with a workaround.

I took a piece of white copier paper and cut a rectangle to the same size as the cardboard reflector. Cutting the paper in half, I was able to slip both halves between the gap in the pins on the bottom of the LCD and position them in proper place. I held them in place with a bit of cellophane tape.

From here on out the rest of the front panel assembly went smoothly. Again I encountered the need to reference the errata for the main encoder knob as Elecraft includes a different unit than the one referenced in the original instruction manual. The encoder in my kit required me to solder a few parts into an auxiliary board to which the encoder was attached. The auxiliary board is then attached to the back of the front panel board.

The last step was to mount the completed front panel board inside of the front panel. Before doing so, the manual lists about 30 resistance checks for the board. Each test point checked out as specified to ground – excellent!

I was very pleased that after I carefully mounted the board the front panel looked perfect. All of the push buttons were a proper and uniform height through the holes on the panel. All knobs, including the main encoder dial, were also correctly mounted and turned with ease. Best of all the main display LCD that caused me so much grief, looked perfect under the front bezel.

The completed front panel…. it ‘looks’ like a radio anyway.

Next up – the RF Board. Stay tuned….

A DIY 555 AM Transmitter

Build this low power dirty AM transmitter and learn about RF modulation.

In the 21st century we have all become accustomed to our connected high-tech lifestyle and we more or less take our internet based social and commercial connectivity for granted until the ‘network goes down.’ Much of the technology that drives our digital being are computer based, but another essential element is radio technology, without which we would find ourselves much less connected.

How does ‘radio’ work?

Long before manipulated radio waves were used to provide the backbone of today’s digital cellular and cloud based information network, those of us who grew up in the twentieth century knew radio primarily as a means to enjoy music, news and talk, via the AM and FM radios in our homes and cars. But what is radio?

Simply put, radio is the transmission and reception of electromagnetic waves that are encoded with data. The data could be spoken word, music, or digital data like text and email messages or larger digital files like software or other data files.

The data that can be transmitted via radio waves exists as low-energy signals and they must be attached to a high-energy signal called a carrier wave in order to be transmitted. A carrier wave is at a significantly higher frequency than the input signal and is typically sinusoidal.

The mixing of the signal with the carrier wave is a process called modulation. There are several ways a carrier can be modulated, the two most common modes of modulation for an audio signal is amplitude modulaion (AM) and frequency modulation (FM). (Another common method of modulation a carrier signal that is beyond the scope of this article is phase modulation (PM)).

Amplitude modulation involves varying the signal strength, or amplitude, of the carrier wave in direct proportion to the message signal. Frequency modulation involves varying the frequency of the carrier wave in dirrect proportion of the message signal.

**AMPLITUDE MODULATION:** A low energy audio electrical signal is mixed with a sinusoidal high energy carrier wave in the transmitter. This modulated signal is amplified and emitted from a transmitting antenna. The modulated signal is propagated through space and can be received by the antenna of a properly tuned remote radio set. The receiver demodultes or removes the carrier from the audio signal which is electronically enhanced and amplified and finally sent to the speaker where it can be heard and understood by the ear.

A simple low power AM radio transmitter

It is possible to construct a very simple low power transmitter built around the ubiquitous 555 Time Integrated Circuit which is capable of demonstrating the principle of amplitude modulation by mixing an audio signal with a carrier signal that can be transmitted to and received by a AM radio receiver.

The 555 timer chip was designed in 1971 by Hans Camenzind and has remained one of the most popular and versatile integrated circuit chips ever produced. Simple when compared to today’s chips which may contain tens of billions of transistors, the 555 has 25 bipoloar transistors, 15 resistors and 2 diodes.

The 555 chip has three distinct modes of operation – monostable, bistable, and astable.

The monostable mode is also known as the one-shot mode and will output a single pulse of current for a specified length of time. The bistable mode is also known as the flip-flop mode and alternates between two stable states, on and off, controlled by the trigger and reset pin.

The astable mode is also known as the oscillator mode and can be used to generate a carrier wave that could be modulated in a model RF transmitter circuit. We will employ this feature of the 555 chip for our transmitter circuit described below.

Traditionally the carrier wave in a radio transmitter is a continuous sinusoidal wave. However, the 555’s output is digital, either on or off, so the resulting wave is a square wave. An alterenating current sine wave is smooth and continuous and is optimal for carrying an information signal, but the square wave will work for our purposes.

**SQUARE WAVE OSCILLATION:** Rapid alternation between on and off signal states produces a square wave signal that can be used as a carrier wave in an RF circuit.

The circuit

I will now present and describe a simple AM radio transmitter circuit that you may wish to construct to observe and demonstrate radio modulation. This circuit design can be found on hundreds of websites oftentimes with small variations component value changes or minor modificaitons to the basic circuit. The circuit I present here is based on the core circuit, nominally modified to reflect what I have found to work well on my bench. I encourage readers who take the time to build my circuit to experiment and share modifications letting us know how you may have enhanced performance.

We will start by looking at the transmitter circuit by its three sub-circuits. The first is the oscillator circuit that produces the carrier wave, the second is the audio input sub-circuit, and thirdly we add the output amplifier and antenna.

1.) The Oscillator

The schematic diagram below is built upon the basic 555 astable circuit and this is the heart of the transmitter. The frequency of the carrier wave output on pin 3 is controlled by how rapidly capacitor C1 charges and discharges. The values of resistors R1, R3 and R4 will determine how quickly C1 charges.

When the charge of C1 reaches 2/3 of the control voltage Vcc, the output at pin 3 goes high. When the charge of C1 discharges to 1/3 of Vcc, the output at pin 3 goes low. Changing the resistance of the RC circuit by adjusting R4 will inversely change the output signal frequency. Increasing R4 will decrease the frequency and decreasing R4 will increase the frequency.

**555 SQUARE WAVE OUTPUT** as seen on the oscilloscope. Adjusting the value of the variable resistor, R4 will change how quickly capacitor C1 charges and discharges and changes the frequency of the wave.

2. Audio Input

When a low energy audio signal is injected at the control pin, pin 5, the 555 will mix the input signal with the signal of the carrier wave and produce an amplitude modulated output signal at pin 3, output.

It is important to note that because the carrier wave generated by the 555 oscillator circuit is a digital pulse wave, where the output goes from completely on to completely off, the modulation of the carrier isn’t pure amplitude modulation, but pulse amplitude modulaton.

The pulse modulated RF signal will not be able to capture all of the fine detail of the input signal and you will notice that as a result, that the sound coming from the receiver speaker will sound a bit choppy and not as pure as you are accustomed to.

**ADDING AN AUDIO SIGNAL TO MODULATE THE CARRIER.** The red components in the above schematic comprise the signal input sub-circuit.

3. RF Amplification and Signal Output

The modulated RF signal is output at pin 3 of the 555. Attaching a simple piece of wire to pin 3 will serve as a crude antenna causing the modulated signal to be transmitted, or radiated into space where it can be picked up by properly tuned radio receivers.

Because this is an exteremely low power transmitter, I have added a single NPN bipolar junction transmitter (2N3904) at pin 3 to perform as an amplifier to boost the output signal strength. The base of the transistor is connected to output pin no. 3 of the 555 and the antenna wire will be connected to the transistor emitter. Power is supplied to the transistor via the collector.

**THE FULL SCHEMATIC OF THE ENTIRE PROJECT.** The blue section comprises the oscillator and mixer sub-circuit, the red section is the audio input sub-circuit, and the green section is the RF output sub-circuit.

**THE COMPLETED BUILD:** This circuit makes for an easy project to complete on a solderless breadboard.
A complete kit wiht all parts shown with detailed instructions is available from the author – see below.

Antenna considerations

An ideal length for the transmitting element for a radio antenna is 1/4 of the signal wavelength. This length gives us an efficient antenna length where the signal will resonate with minimal loss of signal. What would that length be for this transmitter?

Radio wavelength is calculated as the speed of light, (the speed at which RF waves also travel,) expressed in meters per second divided by frequency expressed in Hertz. The speed of light is 299,792,458 meters / second and the frequency range of the standard AM broadcast band in North America is 550 – 1700 KHz. Doing the math we learn that the broadcast band wavelength ranges from 176.3 meters to 545.1 meters.

Dividing these figures by four, we calculate the optimal antenna length for our transmitter would need to be between 44 and 136 meters or 144.36 to 446.19 feet! Constructing such an antenna for a simple circuit would be impractical and costly.

In this build we are using a piece of wire that is approximately one meter or a bit over 39 inches long. Because such a short antenna length is non-resonant and because the transmitter signal output is very week, you will find draping your antenna wire over the radio receiver establishing a loose coupling to the receiver will give you best results.

If you decide to build this circuit you may wish to experiment with different antenna designs to see how the may affect the range of your output signal. You may try a longer wire and another website suggests using a(n empty) beer can as an antenna.

Ham radio operators often make use of coils when antenna space is limited. Adding a tightly wound wire coil will add inductance allowing a physically shortened loaded antenna become more resonant at a longer wavelength. The concept of designing inductance loaded antennas is a concept goes beyond the scope of this article, but there is no shortage of excellent websites available that cover this topic if you are curious and know how to use the Google.

Using the transmitter

Once you have built the transmitter circuit, using it is straightforward and should be fairly intuitive. In addition to connecting the antenna wire to the transistor emitter and draping it over the receiver, you will of course need to supply a control voltage and an audio signal.

I have found that a 9 volt battery works well with this simple circuit as it is compact and will provide plenty of current to drive the circuit. The 555 will work with a Vcc ranging from 5 to about 15 volts giving you plenty of options.

For my audio source, I initially used the audio output from my laptop but have found that using my Activo CT10 MP3 player works much better as the MP3 player puts out a stronger high res audio signal.

Once you have made the above connections, start the audio source music playing and tune the radio receiver to about 600 kHz. Slowly fine tune the receiver up and down until you can hear the audio signal. It should be heard somewhere near 600 kHz, either slightly above or below.

Once you find the signal, try tweaking it by adjusting R4 on the transmitter using either an RF tuning tool or a mini-screwdriver.

Experiment by moving the antenna wire back form the receiver and raising it and lowering it. How does position change the receiver’s ability to pick up the signal?

What are some other ways you can improve the transmitters performance?

Final thoughts

I mentioned above that this is a dirty transmitter. This term means that the output signal is not well-filtered. Transmitted radio waves by nature produce harmonic signals on even multiples of their frequency. In fact, when you are listening to the radio output around 600 kHz, you are actually tuned to the first harmonic as the circuit’s output frequency is somewhere between 200 and 300 kHz (see oscilloscope photo above).

Try tuning the radio receiver slowly up the dial. You ought to be able to also hear the transmitted signal just below 900 kHz and again around 1200 kHz and perhaps just under 1500 kHz. These are all harmonic signals and this type of unfiltered signal would not be acceptable for any FCC licensed radio transmitting station – wheter commercial or amateur. Harmonics can be mitigated through the use of electronic filters.

It should also be noted that it is of course illegal for anyone not holding a valid FCC license to transmit radio signals. A commercial license is required to broadcast radio signals on the US AM band and it is also illegal for anyone to interfere with commercially licensed stations.

If you successfully build this circuit, you will see that it is not capable of transmitting a signal to receivers located more than a foot or two away at best. You should not modify the circuit presented here to further amplify the signal to gain further range.

SOMETHING NEW: COMPLETE SOLDERLESS BREADBOARD KIT AVAILABLE!

If you would like to build this circuit, I have prepared a complete kit that includes a solderless breadboard, all of the necessary electronic components including the audio input jack, the battery snap, pre-cut jumper and antenna wires. I have also written highly detailed and illustrated step-by-step instructions that should guarantee a successful build every time.

The kit requires no soldering with a limited number of step-by-step instructions to make the project easy and fun withe guaranteed success.

For a limited time, the cost of the kit including postage-paid shipping via USPS to domestic addresses is currently $22.00. The complete kit will be shipped in a padded envelope and instructions and documentation will be sent in PDF format via email.

Solderless 555 AM Transmitter Kit

Domestic US Customers Only

$22.00

Thanks for reading and please share your thought and experiences. You may drop me a line at james@ab1dq.com.

73!

Banggood Calculator DIY kit build

Have you discovered the wonder of shopping at Banggood or AliExpress? They are both something of a Chinese version of Amazon.com (in fact the Banggood logo is not at all unlike Amazon’s) – online superstores where you can buy a wide variety of products from electronics to clothes to sporting goods to cellphones to jewelry to automotive parts and so on.

The smiling Banggood and amazon logos
also feature similar color schemes

One can make several arguments – political, risk, quality – for not purchasing from Chinese online vendors, but I can think of two solid arguments why I enjoy shopping there – the wide selection and the low prices.

Both Banggood.com and AliExpress.com sell several DIY (do-it-yourself) electronic kits – such as radio receivers, MP3 players, test bench equipment, digital clocks, ham radio QRP kits and accessories, etc. The variety is fairly large, especially in comparison to what is available these days from US vendors.

When I was a young scrub, Radio Shack sold a popular line of P-Box (perf-box) kits and I pretty much built all of them including the one-tube AM receiver, the indoor/outdoor thermometer, the shortwave receiver, and the “GoofyLight.”

Several of the excellent Radio Shack P-Box kits available in the 1970s which got me started in electronic kit building. Check out the excellent Hack-A-Day page on the Radio Shack P-Box kit to learn more.

For the last couple of decades before they folded, Radio Shack did not offer electronic kits that required soldering and several other companies that produced DIY electronic kits, such as Heathkit and Ramsey Electronics have now too either gone out of business or no longer sell DIY kits.

While there are still some excellent smaller scale firms producing mostly ham radio oriented kits today (Four State QRP Group, QRPme, Elecraft), the easy availability to basic electronic kits, like the ones I enjoyed building as a child, doesn’t exist today.

Enter our Chinese Friends

In recent years I have purchased a few DIY electronic kits from Banggood and AliExpress. My experience has been mostly a good one – the kits are crazy cheap, but sometimes the quality of the parts has been marginal at best.

Another problem I have had building kits from China is reading the instructions. English instructions aren’t always included, and when they are the translations are horribly fractured.

The ability to read a schematic can be beneficial, but may not be enough. I have attempted to construct Chinese radio kits where the schematic did not match the PC board and/or the parts provided. I have also been been frustrated at times to find key identifiers for parts like transformers are identified only with Chinese characters on the schematic.

One interesting hack for dealing with a problem with color coded parts such as RF transformers, that I picked up from a shango066 YouTube video, is to reference the resistor color code chart that might be included the instructions. This makes it possible to identify the parts by the Chinese character for the color in order to correctly place transformers on the circuit board.

*Resistor color code from a Chinese DIY radio kit becomes a veritable “Rosetta Stone” for dealing with other color coded components such as RF transformers :*
*1 = black, 2 = brown, 3 = red, 4 = orange, 5 = yellow, 6 = green, 7 = blue, 8 = violet, 9 = grey, 0 = white, 5% = gold, 10% = silver.*

The Banggood Calculator

Speaking of resistor color codes, what initially attracted me to building this specific calculator kit is that I noticed on the Banggood website that the buttons on this calculator had the corresponding colors of the resistor color code.

The calculator has a mode that will calculate 4 band or 5 band resistor values by entering the color of the rings. (Yes I know that you can easily calculate resistance with the simple table, but this is sort of a cool novelty.)

The calculator has 3 other function modes – basic decimal arithmetic, voltage calculations for LEDs, and decimal-hexadecimal conversion.

I ponied up $13.66 USD and ordered the Geekcreit DIY Calculator Counter Kit Calculator Counter Kit Calculator DIY Kit LCD Multi-purpose Electronic Calculator Electronics Computing with Acrylic Case (yes, that’s the actual product name on the website) along with a few other items to get the total high enough so I could enjoy free shipping. My package arrived on what must have been a not-too-slow-boat-from-China about 2 weeks later.

The Build

One of the great things about this specific kit is that the printed instructions were very good overall and they also included a QR code and the URL for a very well done fully illustrated online step by step assembly guide.

Soldering in all of the components took less than a half hour’s time. All parts were clearly labeled and the online guide pretty much guarantees error-free building. I chose to not use the IC socket and directly soldered the main chip to the board.

The 20 push buttons have four contacts each and I soldered them to the PCB in four column groups of five, tacking down one terminal for each button, then checking to see that it was flush to the board before soldering the remaining contacts The kit comes with 2 printed sheets of key labels which sandwich between a blue button and clear cap.

*The two row LCD attaches to the main PCB via a 16 pin header strip.*

The entire kit took less than 90 minutes to build and I encountered no problems along the way. I did use an ohm meter to confirm the values of the resistors before soldering them in place. The acrylic case went together fairly easily, although aligning the last three screws that hold the LCD in place required a little back pressure with my free hand.

*SPARE PARTS – My kit was complete without any missing parts and the kitter (Geekcreit*) gets big props for including a spare sheet of the the key labels along with spare parts for some of the pieces that typically fly from my fingers and get lost in the carpeting. I opted to not use the IC socket.

Overall this was an excellent project for a Sunday morning at the workbench and now I have a one of a kind calculator that I can take pride in having built myself.

The only criticism I have about the calculator is that in order to change the two CR2032 batteries, you have to disassemble pretty much the entire acrylic case as there is no battery door. As mentioned above, mounting the LCD screen was a bit fiddly so I hope the batteries exhibit a long enough life.

Overall I would recommend this basic kit for anyone who enjoys building such things.

Have you built any DIY electronic kits from a Chinese online retailer? If so, which ones and what have your experiences been? Please drop me a line at james@ab1dq.com.