I hacked the control panel for my Truck's power window switches (long story). So, the way they work - I have to send +12 and GND to two leads to make a window go DOWN and REVERSE polarity to make the window go UP. Right now I am using a big fat DPDT relay to do the work. I want to have it run by transistors, but I am confused with the circuitry.
I've used TIP120's to trigger solinoid valves, but it seems to only take the power in one direction from positive to ground.
Does anyone have advice or know where I can read to help myself figure this out?
The easiest and safest way to do what you want is to buy a motor driver module. I like the ones from Pololu. There are many and to make the best choice you need to measure the maximum current the window motor draws -- do that with a multimeter on the 20A setting and run the window up and down a few times, maybe even with your hand providing some resistance.
If it is less than 3 amps, then this cheap driver will do http://www.pololu.com/product/713
If less than 5 amps, this will do Pololu - MC33926 Motor Driver Carrier
I did do some research on the h-bridge. It is possible. I had trouble finding transistors to handle 30 amp capacity, for a reasonable price, some of them were like $5.00 each (x4 for each window, and 4 windows = $80 for all for windows - just in transistors !?!??).
I found a pre-made h-bridge motor board on ebay was $16, handles two motors with all; the circuitry. two of those boards $32 from China. Still not reasonable cost just to toggle windows to go up and down....
After more research found, power windows only draw about up to 10 amps PER WINDOW and probably 30 amps for all for windows at the same time toggled.
What I did to resolve the situation, was use the 8-channel relay board. It was like $10 or something. Wired that into 4 momentary up/down switches (which are ridiculously difficult for me to find, I had to trash pick from some other control panel).
I think you found the best solution. There are times when the best solution is a time tested electro-mechanical relay, especially at the current levels you are using and the need to control voltage polarity. The main advantage of H-drive is it adds variable speed which doesn't apply to your application.
Yes except I can't get the windows to go up FASTER unless I step up the voltage from 12. I can't see a situation where I would want my windows to go down SLOWER then usual.
The relay board just about barely fits into the driver's door panel.
I think I found some transistors finally at like $1.20 each, so with all the additional circuitry, time and effort - the relay board did the trick.
Yep, relay board is definitely the simplest and most rugged approach for this.
However at 10A, you should be able to construct one pretty cheaply from mosfets, e.g. STP65NF06 for 41c each, though you also need to produce a gate-drive voltage well above 12V, so it gets a little complicated. The FETs would be a good approach if you needed many many outputs and speed control (as you say, reduction) on each.
Erich, the MOSFET uses voltage to drive and has a much higher rating than a transistor.
you will also need to have a way to shut the power off when the motor reaches the end stop. the DC motor will stop spinning and the amps will go way up.
try e-bay for much better deals.
and let me know of you need boards made, I have been having them made by ITEAD and you get quite a few for cheap.
If you don't mind using relays, I have a bunch I can send you. pulled from a lighting control panel.
I dont care about end stops. Ideally, I could put 2 microswitches on each 4 windows, or add additional circuitry to sense a drastic change in current when motor ceases to move from hitting a maximum limit. I don't feel I would need that. I can see the window hits the top or bottom so I just stop pressing the button.
I never used the automatic up/down on the original interface, it was a distraction. It always was going all the way up and down automatically and i just manually adjust 1/2 back up again anyway.
However.... When I DO free up time between the other projects, it would be nice to automatic roll up all the windows when the key-out was sensed, locked doors was activated.
You'll care about end stops when the fuse blows. While the motor draws 10A normally, it could easily pull 50A+ stalled. Consider what happens when you're winding two windows down at the same time and they hit their stops...
What is a polyswitch and how does that work? Does it NOT involve me running 4 more wires all throughout my truck back and forth for each window and using up another 16 hours of distraction time?
I am about the auto-sense current drop switch. If I can avoid running 20 more wires with 50 more terminal connectors and 100 more solder splices with 200 more other distractions, that would be great.
I would rather learn how to detect drop current programatically then fish wires all afternoon.
A polyswitch is a self-resetting fuse. Put too much current through and it will go open, then you have to wait a little while it cools.
Current detection isn't too hard: put a small (0.05R) resistor in series with the load and when the voltage across the resistor climbs too high, your current is too high. Arduino built-in ADC can monitor that and cut the power appropriately.
As a crude form of protection, a polyswitch could replace a fuse. It would work quite well, they self-heal or reset in less than 1 second. However, this is crude in the fact that if a circuit has a continuous short or problem, the polyswitch will keep resetting and tripping and eventually drain the battery. That's why you see them protecting the devices in a circuit rather than replacing the fuse.
I've used a 7A polyswitch to charge a 1.5 Farad capacitor (5 years ago) - never had a problem.
In various electronic circuits I always use them when possible (I've used probably over 1,000) without a failure, so reliability is quite good.
You could go with polyglot, polyswitch or both - your choice (couldn't resist ;))
Not having any trouble blowing fuses. I've had it in the truck for quite a few weeks now, rolling windows up and down - the setup works without any trouble.
