Producing special cables

To connect different components, special cables have to be produced.

Time required

Building: 30 minutes

Tools required

soldering iron
heat shrink tube

Parts required

for DHT:

3x Cable ca. 65mm (red, yellow, black)
1x Cable ca. 30mm
1x 4.7 kOhm (yellow)

JST Pinout

Power-Module -> CM4

This cable connects the power from the power module to the CM4. Use the JST GHT and the fitting, crimped cables and put it together. There is a +5V supply on pin 1&2 and ground on pin 3&4. We combine each of the two pins to get enough power for the CM4.

DHT22 -> CM4

This cable also connects the DHT22 sensor (humidity and temperature) to one pi.

DHT22 -> Raspberry Pi Zero

To meassure the air temperature and humidity on the inside of the Box, a DHT22 sensor needs to be attached to one of the Pi's.

First solder (red) vcc cable and the resistor to the DHT as shown

2. Solder the 20mm cable to the data Pin and shrink the first DHT pin.

3. Solder the open end of the resistor, the open end of the 20mm cable and the long data cable (yellow) together.

4. Attach the (black) GND cable to the last Pin, and cover your bad soldering points with shrinking tube.

Power Switch -> Power Module

Solder two precrimped JST-GH cables (~20cm long) to the power switch as follows

Insert the cable ends into the JST connector. Insert at pin 1 and pin 4 of the JST connector.

Isolate the cables at the switch side
- Using hot glue
- !! Special caution needed on the lenght of the isolation at the switch side !!

PixRacer -> CM4 Telemetry

The next step is to build the cable for the telemetry connection between Pixracer and the CM4. Therefore the JST GHT is needed. Moreover you need a wire, because each Pi needs to be connected to the PixRacer. There need to be 3 wires in the JST GHT.

PixRacer -> RC-Receiver

The cable connects receiver in the plane (FrSky R-XSR) to 2 ports ob the PixRacer: RCIN and FRS.

You need:

From FrSky-Receiver:
- Plug with 5 cables
- Remove the white one
From PixRacer:
- JST-5 connections (fitting the RCIN connection)
  JST-4 connections (fitting the FRS connection)

Cable must be drilled!

How to test

connect to PixRacer
connect to receiver
bind the remote control to receiver
check connection
check telemetry
- Long Press on "PAGE"
- See the telemetry from the PixRacer

RFD 868+ telemetry radio -> PixRacer

from https://www.hs-augsburg.de/homes/beckmanf/dokuwiki/doku.php?id=searchwing-rfd868-mount

The modem is connected to the PixRacer Telem2 port and the power module. The modem is mounted in the right fuselage half and will be connected just shortly before glueing the two fuselage parts to the PixRacer and the Powermodule.

UART cable to PixRacer

Use three 12inch precrimped JST-GH cables
Remove the JST-GH crimp at one side
Remove 3-4mm of isolation to crimp a Harwin M20 crimp
Crimp a Harwin M20 connector
Use a Harwin 8 pin connector and put the crimps in the connector according to the following image

Compare the connector to the RFD868+ connections at the modem.

Remove Pin 15 of the RFD868+ modem. This will be the safety pin to avoid wrong mounting of the connector.

Solder the pin in a Harwin M20 connector and insert that connector in the Harwin housing. Fill the other four open places with empty Harwin M20 connector to increase the holding force of the connector.

Mark the RX and TX and GND cables and then weave the cables such that they are closer together. Now take a JST-GH 6-Pin connector and insert the pins according to this image

Pixracer pin layout: https://docs.px4.io/v1.9.0/assets/flight_controller/pixracer/grau_setup_pixracer_top.jpg

Please note the different directions of the connector/cables in the labeling.

Pin layout of the Pixracer:

Pin layout to the RFD868+:

Note the difference between the yellow cable named TX on the board and RX on the connector!!! The name RX for the yellow cable on the JST-GH cable connector refers to the RX on the RFD868 modem. Please remember to connect the RFD868+ TX to the PixRacer RX and vice versa. So according to the following table: