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arunb
Joined: 08 Sep 2003
Posts: 492
Location: India
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| Using a PIC 16f628 to vary the resistance |
 Posted: Thu Aug 12, 2004 1:04 am |
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Hello,
Is it possible to use a PIC 16F628 to vary the resistance in the range from 100 Kohm to 1 Mohm.
Some options are as follows.
1. A stepper motor and a variable resistance.
2. A digital potentiometer ( But the Microchip range is restricted to 100 K only).
Kindly advise...
bye bye
arun |
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Ttelmah
Guest
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| Re: Using a PIC 16f628 to vary the resistance |
| Posted: Thu Aug 12, 2004 2:47 am |
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| arunb wrote: | Hello,
Is it possible to use a PIC 16F628 to vary the resistance in the range from 100 Kohm to 1 Mohm.
Some options are as follows.
1. A stepper motor and a variable resistance.
2. A digital potentiometer ( But the Microchip range is restricted to 100 K only).
Kindly advise...
bye bye
arun |
Lots of different ways really. You can build your own version of the digital pot (it is just MOSFET switches, and a resistance 'tree'). You can also simply use a FET as a variable resistor in it's own right, by varying the drive voltage to it.
I have done a similar thing with the latter circuit in the past, using an opto-coupled bilateral switch, and measuring the resistance being produced (with a current sensor), and then adjusting the control voltage to give the required current. This was necessary, because of the non linearity of the drive element in this case. There are opto-couplers available, which are designed for use as analog couplers, where there are two driven' elements, one on the primary side, and a second on the output side, which are closely matched. You then adjust the feed voltage, till the right result is being seen on the 'primary' element, and you have allmost the same result on the secondary part.
I'd say you need to give us an idea of the accuracy/number of steps required, the voltage range involved, and the nature of the signals (AC/DC etc.)?. Also the rate of change needed, the likely enviroment, and the number of changes involved?. These all affect the likely solution.
At the low currents presumably involved, you could simply consider the 4066 quad bilateral switch. The typical 200ohm 'on' resistance, will be insignificant.
Best Wishes |
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