Hi,
TLDR version:
I have the following circuit, it have a some sort of resistor devider that I'm not able to understand what is it,
and how is it connected inside to properly reverse engineer the circuit.
Long version:
I'm working on a alternative control circuit for a Tape Deck of my old mini system. (ASP/volume control and amplifier, CD, RADIO are all broken, the tape drive is the ony partially salvage part of it)
The tape type, record protect, tape presence is read by some micro switches that are connected to a resitor network and via an ADC I can read the state.
What is driving me crazy is identifiing the resistor network component internal topology.
I've applied 5V and GND to its last pin as by schematic and I have identified some sort of resistor ladder, but after a lot of measurements i cannot figure out how is it topology:
PIN 1 is VCC (4.998V)
PIN 2 is ADC_OUT (4.620V)
PIN 3 is a button (4.956V)
PIN 4 is a button (4.942V)
PIN 5 is a button (4.907V)
PIN 6 is a button (4.836V)
PIN 7 is GND (0V)
Then I've started on measuring its resistance between pins:
1>2: 27K ish
1>3: 4.5K
1>4: 4.5K
1>5: 4.5K
1>6: 4.5K
1>7: 77K
2>3: 26.85K
2>4: 29.12K
2>5: 30.06K
2>6: 30.61K
2>7: 92.95K
3>4: 8.75K
3>5: 8.84K
3>6: 8.94K
3>7: 80.64K
4>5: 8.75K
4>6: 8.86K
4>7: 79.63K
5>6: 8.75K
5>7: 78.53K
6>7: 73.84K
So far I'm simply mapping each of the 16 states to its switch combination inside the mcu, but the threshold from the ADC are so near that sometimes a switch is cofused with another one.
So probly there is a better/simpler way once the resitor magic is resolved.