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Wired remote control...

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Duvig123

New Member
I'm new to this, so I will try to be as clear as possible. I want to make a control interface for 12v DC that will use a membrane switch interface and have led indicators and a 2 digit 7-segment display.

I am trying to control and existing Motorola maratrac radio head and several different 12v appliances in my car and don't want to have too large a control pad. I think know how to wire the membrane switches and the leds, and the 7-segment I will just be working off the existing one on the mobile radio.

My problem is that I don't want to run a separate wire between each switch and it's respective relay. The controller will be right next to the driver seat and the relay box will be in the trunk.

How can I convert all my switching signals into a single digital transmission that can then be sent using only CAT5 cable and then be decoded at the other end to control separate relays?

I plan on doing the same thing in the other direction to control the LEDs and the 7-seg.

I am fairly good at basic electronics; wiring and soldering, but I don't know that much about IC, so please bear with me. Anything you say will be looked up in a dictionary!
 

duffy

Well-Known Member
You need something to convert from parallel to serial and back again. On the receiving end, this is pretty simple for a bunch of relays - just some shift registers, basically. Put some little drive transistors on each output to drive the relays, good to go. There would be 3 wires - clock, data and a latch signal. Maybe a ground to avoid noise. Get the power from the car at each end.

On the transmitting side, it's a bit trickier. You need parallel to serial conversion, a clock, something to send the latch signal after the final pulse, and if that membrane switch is matrixed, you are going to need to read a switch matrix, if you are trying to sync up with an existing thing that's trying to read the matrix, it could be a real *****. Doable with a microcontroller, but it's a fair amount of circuitry for discreet logic. You would need parallel to serial shift registers, binary counters with presets, couple of 555's, not sure what else.
 

Duvig123

New Member
I understand the Scematic, However, what kind of IC do I need to convert 8 bit parallel to one serial signal?
 

duffy

Well-Known Member
That would be a UART, if you want just ONE wire. Asychronous transmission.
 

Duvig123

New Member
Is it at all possible to use PICs to Communicate serially with one another? If so, What kind should I be using?
 

duffy

Well-Known Member
Yes, PIC chips are used that way all the time. Any of them will work, because even if it doesn't have a hardware UART, you can put a software UART in it. I think I might use a PIC18F4520 for it because it has a hardware UART and a bunch of ports for I/O to drive all those relays and fits in a regular 40-pin dip socket that can be put into regular .1"x.1" perf board.

But maybe a smarter way to do it would be to get a prototyping board that already has a pic chip on it and comes with the software to program it. That "blueroomelectronics" guy on here designed one, costs less than fifty bucks, runs on +12V, has a UART and some general purpose I/O lines -
blueroomelectronics Inchworm+
Ask him for more details.
 
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blueroomelectronics

Well-Known Member
Hi Duffy the Inchworm+ is only a programmer not a project board.

The Junebug is both a programmer and a PIC tutor, even has an IR detector for TV remotes.
 

duffy

Well-Known Member
Wait - there seems to be an error in your title block on that page. Check the HTML, it's for the wrong kit.
 

duffy

Well-Known Member
Nah, he's got it in the trunk.
 

Video Warrior

New Member
No problem, just run a wire from the controller head (once you decide what the various "control codes" will be) to an IR emitter in the trunk. Shoot out the signals in infrared to your IR detector/relay actuator.

Or wait. Maybe it'd be simpler to just connect the wire from the head right to the relay controller.

Cars are a noisy environment for people too.
 
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duffy

Well-Known Member
One wire and ground. I think an asychronous signal will survive even without an RS232 level translator. Need to have a LOT of junk in the trunk to make this approach easier than using, say, a DB25 cable with full breakout and wiring each one separately.
 
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Duvig123

New Member
duffy, that was the whole point. I didn't want to have to run a db25 all the way to the trunk, I would prefer using rj11 or rj45, they are much easier. also, in order to use my Mobile radio, I need to run a cat5 anyway, so I figured I could just use the Free wires from that.

Besides, this project was also meant for me to learn more about IC!

It sounds like the the Junebug might be a good idea, I'll check it out and see if I'll be able to implement it.

BTW, the idea for this system was from the FedSig Smart siren. A freind of mine is a vollyEMT and uses it in his car. I don't need a siren and I am not running lights, I just want to be able to control power to my HAM and my inverter, as well a interior lights for the rear seat from the front of the car w/o having to completely take apart my car and w/o a bulky controller. I figure a custom Membrane and LEDs will do the trick.
 
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