Threshold settings using Pushwheel Switches

[gary36]

I have an analog comparator, whose threshold should be variable from 1mV-9999mV. Condition is that , this setting should be nonvolatile in nature. I have been thinking various options including potentiometer , pushwheel switches + DAC . The issue with pushwheel is that , ganged version is not available in common. is there a better way to set threshold?. (I cannot use any controller in this project)

 

[d123]

Hi,

Is that a trigger threshold? I don't know much about comparators but if so, 1mV seems maybe unrealistic in the real world. Trimpots drift a lot maybe for a nonvolatile setting, perhaps even if the trimpot is used for some kind of one-time calibration and the screwhead glued in place after - I guess the application has no movement or vibration; they also drift a fair bit with temp.

Sorry I can't offer an especially usefully helpful answer.

 

[FvM]

As there's no DAC with BCD input, you need decimal to binary encoding logic at least. If implemented by processor, PLD or huge discrete IC circuit is a matter of taste. Potentiometer with 4 decades resolution is demanding.

 

[gary36]

What is the best settings possible using a precision rotary pot? can we achieve 10mV ( 0-10V range)? Besides I wass thinking of LUT to convert BCD to binary, but unfortunately parallel EEPROM have become obsolete.

 

[KlausST]

Hi,

can we achieve 10mV ( 0-10V range)?

This is 1/1000of full range.
A standard pot has about 300° rotation angle. So can you adjust the pot's wiper precisely down to 0.3°?

Klaus

 

[gary36]

Ok, it is clear. How about LUT method?

 

[KlausST]

Hi,

A BCD switch has 4 outputs. With the significance of 1, 2, 4, 8
One could connect
MSB to a 10k resistor
Bit 2 to a 20k resistor
Bit 1 to a 40k resistor
LSB to a 80k resistor and use an Opamp circuit to generate an analog voltage.

Do this for all four BCD nibbles.

Then use another OPAMP to add the 4 analog voltages but with significance of 1, 10, 100, 1000

You need very precise resistors, good OPAMPs and I recommend to use a voltage reference, because the supply voltage isn't stable enough to get good results.
*****

I wonder why you asked about 10mV of 10V, because this is only three decades, but before you speak about four decades.

Klaus