home    builders    Search

buildersTNC-PI ➜ TNC-PI Kit Ordering and Assembly

page modified May 25, 2018

TNC-PI Kit Ordering and Assembly

This page details the assembly of the TARPN version of the Coastal Chipworks TNC-PI kit Rev 2.3.
For older (red board) TNC-PI versions, see this page for assembly instructions.
This page describes the assembly of green TNC-PI Printed Circuit Board labelled with Rev 2.3 or 2.3a.
If your board has a different silkscreen, see this page.
The TNC-PI is designed, packaged, and sold as a kit by Coastal Chipworks.
See below for a link to purchase the TARPN-tailored version of the TNC from Coastal. The TARPN-tailored kit is shipped with the 10-pin header and with a CPU preconfigured for I2C operation as per TARPN setup instructions.
See the Coastal Chipworks webpage for generic TNC-PI.

Buy the TARPN Version of the TNC-Pi Kit with preconfigured I2C mode
$43 each plus shipping

from Coastal Chipworks
in Fredonia NY

assembled_tarpnv2_1tncpi_i6_07179x261 allparts_i6_07103x800

This kit isn't particularly difficult compared to any other beginner kit.

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.
⇒  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.

⇒  All parts are inserted from the silk-screened side of the board, i.e. from the side on which the white writing is printed.
⇒  Except where specifically noted, all two pin components are non-polorized so you can put the part onto the board with the pins in either hole.

Install parts in this order:

1 X1 3.57 MHz crystal
x1_i6_07056x200 XTAL_i6_07060
2 X2 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.

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

4 R5, R11, R14,
R16, R18
10K resistor
Brown, black, orange

5 R1, R2, R3 100K resistor
Brown, black, yellow

6 R4, R17, R19 1K resistor
Brown, black, red

7 R8 24.9K resistor
Red, yellow, white, red, brown

8 R9 9.31K resistor
White, orange, brown, brown, brown

9 R10 18.7K resistor
Brown, grey, purple, red, brown
Inspect the soldering around R10 and make sure you do not have a short between R10 and R11
10 U2, 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.
11 TX TEST pushbutton, 4-pin
Carefully wiggle the four pins through their holes. Don't put excess pressure else they bend and are hard to put back.
The switch is not square. Rotate the switch so the pin cups are pointed left and right across the board.

12 C9, C10 18 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.

13 C12, C13 22 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.

14 C7, C8 0.01 f 2.5%
Red and yellow or grey; if grey marked 10 nF
While non polorized, these parts are not symmetrical. There is one orientation where the two parts won't fit side by side. Rotate the two parts individually so they both fit snuggly against the board, then bend the leads apart, and then solder.

15 C3 100 pf
C3_i6_07026x190 ceramic disk 100pf
labelled 101
ceramic disk or dipped

16 C1 10 f 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.

18 Q1 PN2222 transistor
orientation is important!
Line up part with silk-screen.

Do not confused with U1

19 U1 Regulator MCP1700-3302E
3 pin
orientation is important!
Install so the flat side is toward the edge of the board.


20 JP2 2 x 5 header
Insert on top, solder from bottom
Short pin goes down through the board.
Long pin side is up.
See pic on left.

21 Power up and test voltage

voltage_test__v2_3_573x800 volts_i6_07092x600
22 D5
Yellow LED (DCD)
Orientation is important!
Notice that the LED silkscreens show a flat side.
Make sure the squared end of the LEDs
line up with the silkscreen.
Ensure the shorter leads on the LEDs go through the holes closest to the flat side of the LED outline.


23 R6 and R7 10K trimmer potentiometers
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.
Using a screwdriver, set the potentiometers to about the middle of their range.
A feature of the TNC-PI uses R6 TXDELAY to erase the I2C programming. If R6 is set fully counter-clockwise (off) when the TNC-PI is reset or powered up, the TNC-PI will erase its I2C address programming.
Set both potentiometers to middle until the Configure TNC-PI process!


24 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.
25 U2 CML MX-614 Modem
16 pin IC
26 U3 PIC16F1847 microcontroller
18 pin IC
27 U4 MCP6023 Op Amp
8 pin IC
28 U5 23K640 Memory
8 pin IC

30 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↝2018 -- all rights reserved