radiopad.txt

20-pin connector
1 -
2 - 5V
3 -
4 - GND
5 - PLL control DO
6 - PLL control CK
7 - PLL control LE
8 - RX enable
9 - PA enable
10 - (CPU Reset, active low, 4.4V)
11 -
12 - (Modulator high frequency input? 5-7V, if modulation not needed, connect to GND)
13 - TX enable
14 -
15 - RSSI? (for squelch functionality connect to receiver IC pin 12 and potentiometer to GND)
16 - Demodulator audio out (for squelch functionality connect to receiver IC pin 14)
17 -
18 -
19 - (Modulator low frequency input? 1.1V, if modulation not needed, connect to GND)
20 -

(Modulator audio input - point 3 on bottom side.)
Modulator audio input - Pin 10 of TL064C on bottom side.

Connect MCU pin 68 to VDD


Receiver IC MC3371 https://www.nxp.com/docs/en/data-sheet/MC3371.pdf
PLL IC MC145191 https://datasheet.octopart.com/MC145191FR2-Freescale-Semiconductor-datasheet-13710712.pdf
Desolder NEC uPD70320G, NEC 710510B and MAXON IC's