N2IRZ RSSI Board v1.5 Assembly

Page modified March 10, 2025

Specifications may change without notice.
Do not use this device in any situation where loss of life or property would be the result of the device misbehaving or failing. If you go beyond this rule, you are self-certifying this device. This device is built by hobbyists for a hobby project. We do not certify that this design, or any particular unit, is sound. Use at your own risk.

Feel free to use any of the images on this page for publicity or articles! Commercial Use is Prohibited.

Note that some of these photos are of a pre-release version of the board.

N2IRZ RSSI Board Kit built March 2025

New kit builder?

If this is your first time building a kit, or need some guidance on soldering, please visit The Adafruit Guide to Excellent Soldering. Very highly recommended.

Of course, finding a neighbor, ham club member, or friend with electronics soldering experience is a great resource.

And, there's some great info on soldering at the TARPN website. Scroll down that page a bit to "soldering tips".

Kit Ordering information: Contact N2IRZ via QRZ.COM

Kit Contents

Please carefully inspect your kit to identify and verify each component. See the Assembly Instructions below for photos of each item.

Qty	Item	Designation	Image
1	N2IRZ RSSI Board PC board	Board
15	470 Ohm ¼ W resistors	R1-R15
3	Red LEDs, T-1, 2 mA	D2, D3, D4
4	Yellow LEDs, T-1, 2 mA	D5-D8
8	Green LEDs, T-1, 2 mA	D1, D9-D15
1	0.1 uF monolithic capacitor	C1
1	0.33 uF tantalum capacitor	C2
1	LM7805 voltage regulator	U2
1	3-pin MQS Male header	J1
1	Raspberry Pi Pico	U1.
1	2x7 0.100" header	Header
1	0.1" Berg Jumper	Jumper
1	Pre-crimped 3-wire MQS cable	Cable

What You Will Need

N2IRZ RSSI Board Kit
Multimeter
Soldering iron
Thin rosin-core solder
Sharp diagonal cutting pliers
The Thonny software application (Download It HERE).

Circuit description

The N2IRZ RSSI Board displays the strength of a radio's received signal, much like an S-Meter in most amateur radios. Because TARPN Networks tend to use surplus commercial radios, which typically do not have S-Meters, we use this board as an aid to link diagnosis and performance. Having a Received Signal Strength Indicator (RSSI) helps us in a few ways, including:

When first investigating a path for a potential link, we can easily see the power of the received signal.
When aiming a directional (Yagi) antenna on a link, we can easily determine the direction for maximum signal.
On an established link, we can see if the normal signal level has changed.
With its many blinking lights, it makes for a pleasing link activity display.

The core computing power comes from a Raspberry Pi Pico (1st generation, RP2040). software on the Pico reads in the radio's RSSI voltage and displays a relative value by lighting successive LEDs on the board. These LEDs are driven by raising the voltage on specific GPIO (General Purpose Input/Output) pins on the Pico. Resistors limit the current to the LEDs, protecting both the lEDs and the Pico. An on-board power supply accepts power from the radio (typically 12-volts, allowable is 8- to 18-volts) and converts it to a clean 5-volts for the Pico. A robust automitive-grade signal input connector allows for easy interfacing with the radio. Specially-selected LEDs, rated at a 2 mA current draw, are used to avoid overloading the Pico.

A signal selector area allows the N2IRZ RSSI Board to be used with radios having different RSSI vs Antenna Input Level curves. At this time, the TAIT 8000-series radios and Kenwood TK-x90 series radios are supported; this page will be updated when a radio is added. The user must place the included jumper on the correct header location for the RSSI board to function: A missing header displays an error condition (LED1 & 2 blink alternately)

The software is written in Python, and is downloadable and open-source. If you desire to add or change the software, it would be a kindness to send a copy to N2IRZ at his QRZ.com email address.
The software uses an onboard Analog-to-Digital (A/D) converter to measure the analog RSSI voltage. It then lights a number of LEDs sequentially to visually indicate the signal level. As an aid to recognizing very fast signals, the highest signal level received in the last few moments is indicated with a brief hold time.

The end-user can load new software, provided by N2IRZ, others, or self-developed. The peak-hold time, the voltage calibration - indeed, any aspect of the board's operation - can be customized by anyone who is moderately fluent in the Python programming language.

Assembly and Use Instructions

There are four parts to this process:

Assemble the board
Program the board
Assemble the cable
Prepare the radio

Start with assembling the board!

1. Assemble the Board

Install parts in this order:

1.1

Install R1 thru R15

For this step, you'll need the 15 resistors included with the kit.

NOTE: Your kit may include 1/4-watt or 1/8-watt resistors. Although smaller, the 1/8-watt resistors have an identical function to the 1/4-watt version and are used in the same way.

One at a time, bend each resistor's wire lead as shown, then insert it into the board with the body of the resistor nearest the edge of the PC Board, as shown.
Bend the leads over on the bottom of the board to hold it in place, then solder ONLY the wire lead closest to the edge of the PC Board (body side). Don't solder the other lead just yet.
Repeat for the remaining resistors.

Once the body-side lead of all 15 resistors has been soldered, carefully adjust the resistors so they all stand up straight and even. While alignment is partly for looks (you want the board to look nice) it also helps avoid short circuits and other future problems.

Solder the other resistor wire leads in place, then clip the excess from the bottom of the board.

1.2a

Prepare the LEDs

For this step, you will need the fifteen LEDs and a USB-A connector (as a bending guide). For all fifteen LEDs:

Hold the LED against the USB-A connector edge as seen in the top two photos.
With the SHORTER lead AWAY from you, bend the LED wire leads down.
The bottom two images show the expected end result. Note that this is opposite of the NinoTNC LEDs!

1.2b

Install the LEDs

Install the LEDs into the circuit board one at a time, paying close attention to the LED Color markings on the edge of the board, as seen in the second image.
Bend the leads sticking out the board bottom so the LED is held in place.
Hold the LED so it hangs over the edge cleanly as seen in the third image, then solder ONLY the SQUARE LED Pad, leaving the other (round) pad unsoldered for now. Hold the LED by its plastic body, as the metal wire leads will get very hot during soldering!
Repeat this until one lead of all 15 LEDs is soldered. Double-check the LED colors are in the right places.
Now adjust all the LEDs carefully so they are hanging equally over the board edge, are aligned perpendicular to the board edge, and are vertically in a neat row, as shown in the final image.
Solder the other wire lead, then clip off the excess from the board bottom.

1.3

Install C1

For this step, you will need the 0.1 uF monolithic capacitor.

Note: The PC Board can accommodate parts with a wire lead spacing or 0.1" or 0.2". Be sure to use the correct two holes for a 0.1" spacing part. The 0.2" spacing part uses the two outer holes.

Install C2 and solder it. Polarity is not important for this part. Clip the exceess wire leads.

-->

1.4

Install C2

For this step, you will need the 0.33 uF tantalum electrolytic capacitor. Here, the polarity is important: On the capacitor body, there is a marking for +, so be sure this wire lead (which is longer) goes into one of the two holes marked + on the PC board, and the shorter lead goes into the unmarked hole (closest to the "C2" text).

Note that the PC Board can accommodate parts with wire lead spacing of 0.1” or 0.2”. Be sure to use the correct two holes for a 0.1” spacing part, while the 0.2” part uses the two outer holes.

Solder and clip the leads.

1.5

Install J1

For this step, you will need the J1 male connector body. Install J1 by snapping it into place on the board, then soldering the three pins.

1.6

install U2

For this step, you will need the LM7805 voltage regulator. Install the U2 voltage regulator, for which polarity is important: Make sure the metal tab on the voltage regulator is facing the edge of the PC board. Solder one lead, bend the part so it is exactly upright, then solder the other two leads. Clip off the excess.

OK, now take a short break

Carefully inspect the board, making sure every part is properly soldered, all polarized parts (All LEDs, C2 and U2) are installed in the correct orientation, and nothing is missing. For the LEDs, if you look inside the LED's plastic housing, you can see the metal carrier wires with their unique shapes; these should all face the same way.

Apply a DC voltage around 13 volts to the "+13v" and "GND" contacts on the board and measure the regulated voltage at the "+5v" contact. It should be very close to 5 volts. IF IT IS NOT, check the orientation of U2: The metal tab must face the edge of the board.
Once you are sure all is as it should be, continue.

1.7

Install U1

For this step, you will need the Raspberry Pi Pico. Install U1, the Raspberry Pi Pico. Note the orientation, with the USB connector at the edge of the PC board. Installing this incorrectly can permanently damage the Pico, and once installed it is nearly impossible to uninstall.

Use some wire (or similar) to align the holes in two corners of U1 with the holes in the PC board. With the board aligned properly, solder two of the Pi's edge contacts to the PC board, then remove your alignment wires.

For this, we recommend holding the soldering iron about a millimeter (1/25") from the contacts on the PI, but firmly placed on the PC board pad. Apply solder to the pad and soldering iron at the same time - look at the image. This will allow solder to coat the pad, which will then wick up to the castellation on the edge of the Pi. This may take some practice, but it is not difficult.

Avoid overheating the Pi by limiting soldering time to about 3-4 seconds per pin. If soldering isn't correct, wait several seconds for the area to cool, then try again.

1.8

Install the Header

For this step, you will need the 2x7 0,.100" header. Install it and, while holding it into the board with a finger, solder any one pin that is not touching your finger (it gets hot!). Verify that the header is tight against the board, resoldering that one pin if needed. Then solder the remaining pins.

This completes the board assembly. Please continue to the next step to load the software onto the board.

The image below shows a Berg Jumper installed; it is yellow for better visibility in the photo, the one included in the kit is black.

2. Program the Board

Follow these steps to load the software on to the Pi Pico:

2.1

Install Thonny

If you don't have the Thonny software application (Supports Windows, Mac and Linux), then please Download It HERE, then install it.
NOTE: The Windows version of Thonny is shown here; other versions should be similar.

2.2

Install Micropython

Visit the Raspberry Pi website and follow the instructions there to "Add the MicroPython firmware".
Alternatively, you can load it using this method.
In BOTH CASES, you are loading the software on to a Pi Pico/Pi Pico H. Be sure to choose that software, NOT the version for Pico W / Pico WH or any Pico 2.

2.3

Dowload and Install the RSSI Software

Download the RSSI software from HERE
Unzip the file, then open the "..._py.txt" file in Thonny. It is delivered as a text (.txt) file to avoid file extension conflicts. Rename it to ".py" by replacing the underscore with a period, and erasing the ".txt" extension.
Note that now the file is a Python file, which can be read and manipulated - but we advise against that unless you are sure of what you are doing.
Making sure your Pi is recognized - in this image it is seen as connected to virtual serial port COM15 - select "File / Save As" (Ctl-Shift-S). Your COM port assignment will likely be different from what is shown here.
NOTE: We have seen cases where the Pico is not recognized; in these rare cases,switching to the "MicroPython (RP2040)" entry on the list seems to restore access. Not sure why though...
In the dialog box, select "Raspberry Pi Pico" and save the file as "main.py".

This completes the software installation.

We can now test the software to see that it is responsive

Reconnect the +13v and GND as explained above, just before step 1.7. The green Power LED should light.
Touch the RSSI contact, located between the +13v and GND contacts, with your finger (perhaps the contact on the bottom of the board is easier to touch). Some or all of the LED indicators should light.
If the LEDs are unresponsive or the green Power LED does not light, either there is a fault in the assembly, or the software is not running. In these cases, ask for support on the TARPN Discord page.
If the two left-most LEDs (green and red) are flashing alternately, you don't have the Berg Jumper installed. Please install it on Position A for now.
If the LEDs respond as expected, continue to assemble the cable.

3. Assemble the Cable

Follow these steps to assemble the RSSI cable to your existing Radio-to-TNC Cable. Note that the specifics differ according to the radio type.

If you have not yet built a radio-to-TNC cable for your setup, visit the TARPN page appropriate for your radio for information on building one.

TAIT 8000-series Radios

Open the DA-15M connector that attaches to the TAIT Radio.
Solder the wires on the RSSI cable as follows:

The BLACK (ground) wire to Pin 15 of the DA-15M
The RED (+13v) wire to Pin 8 of the DA-15M
The GREEN (RSSI) wire to Pin 6 of the DA-15M
The White wire, if visible, is not used

Add the RSSI cable to the strain relief system
Reassemble the DA-15M connector shell

Images coming soon!

Kenwood TK-790 Radios

NOTE: This should also work for the TK-690, but it has not been tested.

Open the DB-25M connector that attaches to the TK-790.
Solder the wires on the RSSI cable as follows:

The BLACK (ground) wire to Pin 18 of the DB-25M
The RED (+13v) wire to Pin 14 of the DB-25M
The GREEN (RSSI) wire to Pin 1 of the DB-25M
The White wire of the RSSI Cable, if visible, is not used

Add the RSSI cable to the strain relief system,
Reassemble the DB-25M connector shell

Note that Pin 13 (TXA), Pin 7 (GND), Pin 15 (PTT) and Pin 16 (RXA) should already be connected (to the TNC).

This image shows a fully-populated DB-25M connector with the pin signals labeled.

4. Prepare the Radio

Some information about preparing your radio to deliver the signals the RSSI Board needs:

For the TAIT 8000-series radios, no additional preparation is needed.
For the Kenwood TK-790 radio, follow the instructions found here on the TARPN website. In particular, see section 7.

This website is maintained by Don Rotolo, N2IRZ. Contact me via the information on QRZ.COM
Updated 10MAR2025

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