I recently ordered a MUX board from my local Ecumaster supplier.
I then wired everything up (3d printed a nice enclosure for it), only to find out that the default state of all (MUX)switches is ON. I checked the wiring (+5v, AIN, GND), all is fine.
I then took the board out again and started measuring on the board itself. Below is schematic diagram of the board.
If I measure across +5v and SW1, I should measure 12.200Ohm’s of resistance, right?
Likewise, If I measure between +5V and SW2, I should measure 6.900Ohm’s of resistance.
However, I’m measuring about 10K ohm on all three circuits.
So, I ordered another board from Ecumaster…same thing.
Am I missing something or is the second board also bad?
U are right…just asking. Cause if u wire the mux board like in the emu scematics there is the risk that u connect sensor ground to a other ground and read nothing.
I don’t think so. I tried it anyway, and it makes no difference.
I still have 1.8v on analog 4 with all switches off…there’s definitively something wrong with the board.
if one just measures the board out of the bag with an ohmmeter placed across a non-ground switch pole and the adc output, it is normal to see 12.2k ohms on all channels. this is bc the mux circuit is not purely passive and instead includes three n-fets, one for each switch. all fets are off if insufficient voltage is applied to vcc (eg. 5v), so the ohmmeter is only reading the series resistance values of the lone 2.2k resistor summed with the 10k resistor that is on the high side of the voltage divider that controls the n-fet gate on/off.
since what can be measured out of the bag can appear to deviate from expectations that are based on the purely passive diagrams generally available, below is the basic circuit as deduced directly from the board components and their layout. so there is a little more going on, which is why the mux board function/cost is more than that of just a few discrete resistors.
