DIGITAL DECADE LEADER

Hi all

How a desired resistance is generated digitally ?

See this for example .

What component is used to generate a fixed desired resistance digitally ?

Thanks
Elico

Look up the term digital pot, there are lots of examples using an arduino.

Alternatively you can use an analogue data selector to switch resistance values in and out of a circuit.
Are you trying to make one of those boxes?

This isn't a digital pot since it has a range of about 8 decades. Its a decade box - but switched with
analog switch chips rather than mechanical switches. It just has enough high-accuracy values to cover the
ranges, 1,2,2,5,10,20,20,50,100,200,200,500 etc. The lower value resistors will have decent
low-on-resistance MOSFETs to switch them in and out, the larger values will use standard analog
switches. The software in it compensates for the on-resistance of the various switches to get
better accuracy.

For that device, given the very large range of resistances and supposed resolution of values, it is unlikely to be discrete resistances switched in/out (think how many you'd need for 0.1? over 1?-24M?), nor a digital potentiometer which wouldn't normally have the kind of range (as it's simply discrete resistances switched in/out). Plus the 1W power rating would mean the resistors used wouldn't be particularly small.

It's far more likely to be some form of MOSFET arrangement driven by a high resolution voltage source to vary the gate voltage and thus the resistance between the drain and source.

It's far more likely to be some form of MOSFET arrangement driven by a high resolution voltage source to vary the gate voltage and thus the resistance between the drain and source.

Give over, it is not.

How a desired resistance is generated digitally ?

Generally.. it is a switch of some kind and it is driven by a PWM signal. The duty cycle of the switch determines the 'resistance' by the duty cycle of the driving signal... Generally...

Bob

Grumpy_Mike:

It’s far more likely to be some form of MOSFET arrangement driven by a high resolution voltage source to vary the gate voltage and thus the resistance between the drain and source.

Give over, it is not.

Ok, so how would you make a system that had a range of 1? to 24M?, with 0.1? steps? And have it handle 1W, and fit into a pocket calculator? That’s what the specifications state…

That is a typical RTD calibration standard used heavily in the process control world. It's job is to simulate being a field RTD sensor, and used to validate the rest of the "instrumentation loop". It truly is a resistance simulator, but normally is called to work at pretty low current values as they are typically 'driving' one element of a Wheatstone bridge input circuit.

They are typically quite expensive because you are paying among other things for it's stated accuracy and they sell to a limited market volume compared to the consumer market. And of course they tend to be very proprietary in design, you won't usually find a published schematic in it's manual.

Lefty