External control of resistance through use of IR 1

[JedOs]

I need some help with driving a motor externally through infrared trnasmitting. The design that we have for the motor controller uses a potentiometer to control the speed AND direction of the DC motor. The problem is I need to control the resistance just as the potentiometer would from the IR decoder IC, which is pre-programmed. All I can control in this situation is the output of the decoder IC. I am thinking that I will use 3 relays powerd by the the 3 different outputs from the decoder IC each switching to use a different resistance. I am quite confused on this issue, as I don't work in electrical engineering.

 

[logbook]

Emulating a potentiometer (pot) is ugly and therefore the answer is to tweak the design so you don't have to emulate the pot. If the pot is just giving a voltage out then the pot can be replaced by a DAC.

Hooking this circuit together will require detailed knowledge of the parts concerned. What is the output from the decoder: pulse width modulated or static logic lines?

Give us some part numbers and/or circuits and we will be able to help you more.

 

[ScottyUK]

You might have a look at the digital pots available, for example, from Maxim.

http://www.maxim-ic.com/appnotes10.cfm/ac_pk/9

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I don't suffer from insanity. I enjoy it...

 

[JedOs]

Thanks so much for replying guys. I think I may have mis-said my actual intentions. I don't need to emulate the potentiometer. What we were thinking was to have 3 different relays coupled with a logic gate (to make sure only one relay is latched at a time). Each relay will be responsible for passing different resistances of current to circuit. The IC Decoder is PIC12C672 PICmicro® MCU

 

[logbook]

The term "latched" is probably not what you meant in relation to the relays. There is such a beast as a "latching relay" but you almost certainly do not mean that. Three seperate distinct currents is fair enough. Whichever is the lowest current can be left running all the time. This saves one switching device.

Using relays is maybe not the best idea. It is good to use relays when you need high voltage isolation but not good for rapid switching. You are not driving the motor directly but just driving the controller chip. Tell us what the motor controller chip is and we can advise better.

 

[JedOs]

Logbook, the motor controller we are using is the K166 from Ozitronics.

 

[VEBill]

I've got one or more home theatre receivers where the volume control can be controlled by the IR remote control. The volume knob and potentiometer actually turns up or down, driven with a geared motor, by remote control.

 

[JedOs]

Yeah my recievers do that also, pretty neat.

 

[logbook]

Here is a typical circuit to interface to your driver board at the pot. The logic lines are assumed to be 3V or 5V CMOS.

http://www.logbook.freeserve.co.uk/image/engtip.gif