I have a keypad where it has 6 buttons. When no button is pressed the 2 terminals read 5kOhms. While button A is pressed the terminals' resistance becomes 55Ohms, If you stop pressing the button the resistance returns to 5kOhms. The other buttons respectively have resistance of 144Ohms, 294Ohms, 541Ohms, 975Ohms and 2Kohms.

I have a device that has two terminals and can read voltages levels up to 8V and store them in its memory. In idle mode the terminals of the device must have 0V. So for example if i connect a 1.5V for 1 second between the device terminals it will store the voltage of 1.5V. If i connect 3V between its terminals it will store it.

Now i want to connect the keypad with the device so that when i press a button it can recognize it. I constructed a voltage divider for this using 5V and fixed resistor 500Ohms, but when the keypad is in idle mode (not buttons pressed) the device reads 4.5V continuously and thinks its a button pressed. I want to design a circuit so that any voltage above 4.1V to be bypassed to ground, so that when keypad is in idle the device to read 0V. When button A is pressed to read 0.49V and when released to return back to 0V (ground).

Can someone help me please?

 

Possibly something like this?


I've not tried it and as I have only had 2 coffees so far this AM, I may have mucked it up

 

This is a natural to use a UP with A/D and just use keypad in a V divider
and measure the V's and do simple test for range of V for each specific
key closure.

ATTINY85 could do that and if you have ever programmed in Basic there is
a free compiler available from Bascom -

https://www.mcselec.com/index.php?Itemid=41&id=14&option=com_content&task=view


Regards, Dana.