Unfortunately, the radio is very bad, very prone to overload on FM and very deaf on HF bands, so it is almost useless. I decided to play with the digital dial just to see if it was usable with other radios or even transceivers.
The dial module has seven wires, with this functions:
VEC: Module power supply. This is the supply for the module. It accepts from 1.8 to 3.3 volts. This line in the radio is directly connected to the batteries. The current drain is 36 uA turned off (clock shown) and 3.75 mA turned on (frequency shown).
GND: Module ground.
VCC: Module power out. This line is labeled in the radio as VC6. When you press the power on button, the module changes from clock to dial and power up this line. This is the line that supply the CXA1691 circuit. I don't know what is its maximum current, so use it with care or use it to drive a switching transistor.
S/W: Selects the intermediate frequency used and therefore, the local oscillator input. See table below for more information.
A/F: Selects the display mode. See table below for more information.
FMOSC: Input for local oscillators used with 10.7 MHz intermediate frequency.
AMOSC: Input for local oscillators used with 455 kHz intermediate frequency.
Fin = 174 MHz
Fin = 70.24 MHz
Fin = 10.44 MHz
Fin = 9998 kHz
- In all cases, local oscillator must be higher than received frequency: Readout = Input minus IF.
- Logic levels in S/W and A/F inputs are referred to VEC line, so 1 equals to 3 volts if the module is supplied with 3 volts.
- In the radio, the AMOSC signal input amplitude was 20 mV peak to peak.
- Both inputs seems to work from zero up to at least 174 MHz.
- For a logical readout, input must be at least the IF value.
- In case of frequency overflow, only less significant digits will be shown.
- The clock alarm just power up the dial, applying a VEC logic 1 to VCC output to turn on the (original) radio.