The thread for this board is actually here (there was another thread dealing with mic emphasis which this module doesn't do):

/g/BITX20/topic/6374017#34387?
?
The board can be found here on Aliexpress:???


The SSM2167 datasheet can be found here:



Thanks everybody for the suggestions on how to remove the two small SMD resistors.? I am not used to working with such tiny components, but I will give it a go!

A few external components will be needed:

1.? The board runs on 3v-5v. The BITX40 operates at 12v.? I am thinking a simple resistor divider will work given the chip draws 4mA according to the specs.?? A simple resistor to the 12v lines should work (I will try something like 6.8K since resistance of the circuit is around 3K) and then measure voltage.

2.? As noted in one of the comments, bias for the electret mic will be required. I am assuming I can use another resistor to lower the 12v line (copying the circuit in the BITX40 mic connector).

3.? Because of the 20dB (or thereabouts) gain of this chip (it appears the module manufacturer has simply copied the datasheet values) I will need a variable pot on the output (i.e. mic gain control).? I plan to bring this to the back panel of my enclosure.

4.? I will definitely also want a variable pot to control compression on my back panel.? Not sure I need it for the noise gate control.? I will use a trimpot.

I plan to mount the module on a small section of prototype board where I can install off-module components.? Little multi-turn trimpots can be mounted directly on the module for controlling compression (200k) and noise gate (5k).? However, I know amateur ops always want to fiddle with the compression ratio!

I suspect that the junction of pin 6 (with capacitor C3) which is an averaged RMS value of input level could be used to connect (via a resistor) to an arduino analogue input to become a VOX control.? I would like to have a play with this as well to ensure there is enough voltage to be read by the arduino!?? This will need a further mod to my mic (I am using one of those cheap Aliexpress Baofeng mics) as the RX/TX switch is in series with the mic input at present.

73 Mike ZL1AXG