How to count pressing the buttons of an analog keyboard without MK?

Question

Electronics

I'm building a bluetooth module into an old car radio.
I would like to control it from native buttons on the front panel (3 buttons are enough: "play/pause", "prev." and "next"). The scheme of the radio buttons is shown in Fig. 1. The module control scheme is shown in fig. 2.
From the radio you need the buttons "sw103", "sw104" and "sw110"

Fig. 1

Fig. 2

How would you splice them? I don’t want to shove a whole arduino to read the resistance and determine the pressed button. Intuition tells you that you can build something on transistors, but there are not enough skills for inventing. The module is powered from the radio through the stub 78L33, has a common ground with it.

Available components:

Can you please tell me how to implement something like this?

Answer 1

Is it possible to change on the front panel board?

Answer 2

An MK solution will be simpler, more compact and more reliable than an analog transistor circuit. If you really want to, look for a comparator circuit (Schmitt trigger). They will need one for each button, plus one more transistor, so that when one comparator is triggered, all others with a threshold lower are turned off (the output should be a "1 out of N" signal).

Answer 3

From the radio you need the buttons "sw103", "sw104" and "sw110"

There is an ambiguity here. You can understand how " it is these buttons that are allowed to be taken away for the control of the VT ", and how " it is these buttons that cannot be touched, they must be left for the control of the radio ". Which option is correct?
The rest is elementary. We select any 3 unnecessary / unneeded buttons from the radio tape recorder, and disconnect them from the chain of resistors and minus the power supply, but leave their connection to each other (we also leave the chain of resistors untouched). We connect this connection of the buttons to each other through a 10 kilo-ohm resistor to a 3.3 V supply. We connect the other (vacated) contacts of the buttons to those PIOs that, according to the VT block diagram, control the commands "play / pause", "prev." and "next".
Everything, it's done. And no transistors, not to mention more complex things.