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page modified February 24, 2016

Legacy TNC-PI assembly instructions

This page is for assembly of older TNC-PI boards. Please see this page for instructions on the latest boards.
There are 3 models of the board. See TNC-PI General Information for details.

All three models may be assembled with the 10 pin header. Available here from SparkFun and included with the TARPNv2 TNC.

PCB boards v1.2, v2.0, and TARPNv2.1

Click to enlarge
V1.2b TNC-PI           v2.2 TNC-PI            tarpn_v2_0_pcb_i6_06943

The three models have the same parts designators in silkscreen so where parts are common between the three boards, they are labelled the same on each board. For the most part you can follow the instructions for the new 10-pin board and successfully build any of the 3 models. I have highlighted the board‑specific differences in the instructions.
Caveat: My instructions are written for an experienced kit-builder though this kit isn't particularly difficult compared to any other beginner kit. The issue is that I don't know all the things to advise you on up front and a beginner kit would have that kind of advice.

That said, I suggest you use a temperature controlled soldering iron, and rosin core lead solder, 60/40 or some such. Also, don't use flux on the board. Cleaning the board before or after soldering should not be necessary.

The part designations, like R1, U2, etc... are silkscreened on the top of the board. Insert all parts from the top of the board where the appropriate designator indicates. The photos provided may be helpful. Beware that there can be multiple versions of the board and the photos are only of one version. Use the silk-screen as the last word unless specifically directed NOT to in the text.

If there is a step which installs multiple parts, you can put all of the parts into the board in any order, and then solder all of them at once.

The reason for the step‑wise assembly order is so in each step when the board is flipped upside‑down for soldering the board doesn't rock too much, and for some steps you can take advantage of the table‑top to force the parts flush to the board for best mechanical stability. The test step, to assure proper voltage regulator function, is done as early as convenient.

What you will need

  • Appropriate Raspberry PI modified with 3 cuts on the header as shown here:
  • Power supply for the Raspberry PI to plug into the micro-USB socket.
  • Insulation Displacement Connector ribbon cable with 2 or more connectors to power up the TNC-PI.
  • Volt Ohm Meter to check the TNC-PI regulator
  • diagonal cutters

Some of the images on this page can be enlarged and opened in a new browser tab by clicking on them.

Install parts in this order:

1X13.57 MHz crystal
x1_i6_07056x200 XTAL_i6_07060
2X2 20.00 MHz crystal
X2_i6_07059x200 XTAL_i6_07060
Note: Make sure you place X2 into the PCB spot marked for it. There is a capacitor part which is the same footprint and adjacent to the crystal.

3C2, C4, C5, C6,
C11, C14, C15, C21
0.1 μf
Eight yellow non-polorized barrels

Skip this step for GREEN TNC kits.
Note: JP3 and JP4 holes are only present on very few early v1.x PCboards.
For boards where these four holes and silkscreen markings are present, install the two wire jumpers at this step.
Use wire trimmed from one of the yellow caps to create two separate jumpers short between lands.
The 10-pin header is installed later.
4JP3 and JP4scrap solid wire short between holes for JP3 and JP4. See photo

R14 is deleted from the TARPN v2.0, v2.1 and v2.2 PCboard.
Those kits would only have four 10k resistors.
5R5, R11, R14,
R16, R18
10K resistor
Brown, black, orange
R14, not shown, would be on the extreme left edge of the board near X2

6R1, R2, R3100K resistor
Brown, black, yellow

7R4, R17, R191K resistor
Brown, black, red

8R824.9K resistor
Red, yellow, white, red, brown

9R99.31K resistor
White, orange, brown, brown, brown

10R1018.7K resistor
Brown, grey, purple, red, brown
Inspect the soldering around R10 and make sure you do not have a short between R10 and R11
11U2, U3
U4, U5
IC Sockets
One 16-pin, one 18-pin
and two 8-pin sockets
These are usually installed and soldered one at a time. You can either hold the socket with a finger while soldering the two corner pins in, then finish the rest of the pins, or you can insert the socket and then bend out two of the corner pins to hold it into place.
Be careful of the orientation.
They are not all pointing the same way!

Make sure you arrange the sockets so the divit at one end lines up with the markings on the PC board.
Note that some of the sockets are pointed opposite of some of the others. Do not install the ICs in the sockets at this point.
12TX TESTpushbutton, 4-pin
(green boards only)
Carefully wiggle the four pins through their holes. Don't put excess pressure else they bend and are hard to put back.

13C9, C1018 pf
ceramic disk
⇐ When stuffing the capacitors, direct the wires so they don't cross. This will enable you to solder the pads without shorting.

14C12, C1322 pf
ceramic disk
⇐ When stuffing the capacitors, direct the wires so they don't cross. This will enable you to solder the pads without shorting.

15C7, C80.01 μf 2.5%
Red and yellow or grey; if grey marked 10 nF

16C3100 pf
labelled 101
ceramic disk or dipped

17C110 μf Polarized
electrolytic capacitor
Part has stripe on one side with ‑ sign.
The other side lines up with + sign in the silkscreen.
C1_i6_07037x150    C1_i6_07054

slide switch, 3-pin. Orientation doesn't matter.
Red boards have no RX TEST switch.

19Q1PN2222 transistor
3-pin -- orientation is important! Line up part with silk-screen.
Do not confused with U1

20U1Regulator MCP1700-33
3 pin
Install so the flat side is toward the edge of the board.
Note that the silkscreen is in error on TARPNv2.1 boards
u1_i6_07085x340 u1_i6_07084x340

21JP22 x 5 header
2x5 header is available at SparkFun for your 26 or 40 pin kit.
2x5 header is included included with TARPN 10-pin versions of the kit. 
JP2 symbol is sometimes not visible
Insert on top, solder from bottom
For boards with 26 or 40 pin holes, install at the end of the board toward U1 regulator
Note: 2x5 jp2_part_i6_07152x340jp2_board_i6_07148x600

22 JP7V1.1 Red board PCBs and some V1.2 Red board PCBs have a JP7 next to C1. Short this permanently with a loop of wire. This enables VCC to the board.

23 Power up and test voltage
Shutdown your Raspberry PI and remove its memory card. This will keep the file system on the card from getting corrupted if there is any debugging to be done.
Locate the largest IC socket on the board which is U3. It is 9 pins on a side.
Use a ribbon cable to connect the TNC-PI to a Raspberry PI. Make sure the ribbon is aligned so
pin 1 of the Raspberry PI is on the same end of the ribbon as pin 1 on the TNC-PI.
Power up the Raspberry PI without its memory card.
Use a voltmeter to check the voltage between the middle pin on one side of U3 and the middle pin
on the other side of U3, i.e. pins 5 and 14. The voltage difference between the two should be 3.3 volts.
Any voltages between 3.25 and 3.35 will do. Pin 5 is the negative side and pin 14 is the positive side.
We're really only interested that it is 3.3 volts.
Power off the Raspberry PI and disconnect the ribbon from the TNC-PI. Make sure you keep track of your memory card. You can put it back into the Raspberry PI.

If there is a problem, inspect the Regulator U1, capacitor C1 and the 10 pin header. Send an email on TARPN yahoo group if you are still having an issue.
volts_i6_07095x688 volts_i6_07092x600

Remove power from the Raspberry PI.

24 D5 Yellow LED (DCD)
Polarized -- make sure the square end
lines up with the silkscreen. Ensure the shorter leads on the LEDs go through the holes closest to the flat side of the LED outline.
25 D4 Red LED (PTT)
Polarized -- make sure the square end
lines up with the silkscreen.

26 R6 and R7 10K trimmer potentiometer
Orange or blue and white
Carefully wiggle the three pins through their holes. Don't put excess pressure else they bend and are hard to put back.
Green boards before V2.3 do not have R6.

27 DE-9 connector
Push flush to the board. Solder the 2 large pin-pairs on the side holes first while forcing the connector solidly onto the board. This will give you the most robust connector.
Next solder the 9 small pins.

Install Integrated Circuits U2 through U5
You may wish to bend the pins of the four ICs slightly inward to facilitate inserting them into their sockets. Ensure the notch on the top of each chip lines up with the notch printed on the PC board. Also make absolutely certain that you do not mix up the two 8 pin chips and plug them into the wrong sockets.
28U2CML MX-614 Modem
16 pin IC
29U3PIC16F1847 microcontroller
18 pin IC
30U4MCP6023 Op Amp
8 pin IC
31U523K640 Memory
8 pin IC

There is a 6 pin mostly-in-line set of holes marked ICSP (In Circuit Serial Programming) . These holes are left unconnected.

On some red boards there are unused pins marked J.

32 Power up CPU test
Shutdown your Raspberry PI and remove its memory card. This will keep the file system on the card from getting corrupted if the power is removed and re-applied arbitrarily.

Connect up the TNC-PI ribbon to the Raspberry PI, observing proper ribbon polarity.

While observing the the LEDs on the TNC-PI, apply power to the Raspberry PI. The RED and YELLOW LEDs should both illuminate, then the RED goes off, followed by the YELLOW. Some additional flickering may also be observed after the two LEDs first go out.

Congratulations. You’re done assembling the TNC-Pi.
Configure TNC-PI
© Tadd Torborg, 2014↝2017 -- all rights reserved