mgianzero

I was thinking after seeing all the "talent" and resources we have here on RL that maybe we someone could help me with this ...

Below is a circuit board which retrofits our windows for the "one-touch" up and down feature that is found in newer cars (even new Boxster and newer 911's have this). I wanted to know how it works.

Anyone care to decipher and understand how this circuit works and possibly even simulate it using modern day DC circuit simulation software? I pretty handy with computer programming, but my mechanical engineering background leaves me with limited understanding of circuits.

I have ideas for other features for our older 993's, but thought I should learn how this works as a starting point. Any takers?

SuperUser

My employer has a cool free tool:-)
http://123d.circuits.io/

zenithblue993

In about 1 and 1/2 years i'll have my electrical engineering degree and be able to help lol.

IainM

Not quite enough info to really work out whats what.

Looks like 3 relays (big blue things), two small signal transistors (round black things with a flat) a power resistor (big white thing)

The big black thing only seems to have 3 pins so could be a power transistor (looks more like a bridge rectifier)

Lots of small diodes (small black cylindrical 2 wire devices) and a few resistors.

The circuit has to maintain power to the window motor in the correct polarity (up vs dn) for as long as the motor needs to wind. Somehow end of travel needs to be detected to switch off power- can't tell if this is part of this circuit or if that is built into the motor circuit already in the car.

Probably some kind of bistable circuit that applies power until the current drops to zero. Just a guess.

Can you tell us part numbers on the various parts?

M. Schneider

From this distance its tough to call with any certainty. Sorry.

Kika

Marc,

I got my BSEE, but that was in .... 1986, and I haven't done any circuitry in my career.

Having said that, I am guessing that the circuit is designed to maintain current either 1. For a predetermined length of time, and/or 2. Until it senses an increase in the current draw, indicating the window has stopped, and there is now higher load on the motor.

It likely has elements of both.

I think the way it works, is that when you hit the switch, it applies 12v to the motor, and the circuit maintains that voltage for say 3 seconds, then shuts off. I would guess hitting the switch a second time probably interrupts the timer, in the event that you want to halt the window between full open and full closed.

If the window is partially open, and you go to close it, or open it completely, it will not need the full amount of time, thus it probably has logic logic to shut off after either a set time, or an increase in current draw.

I am assuming that there are no optical or mechanical sensors involved.

I think I know where you may be headed with this.
Assuming my hypothesis is correct,
Yes the timing can be changed to increase or decrease the amount of time, and yes, the current level can be changed.

The timing is probably set by what is known as the RC constant, a combination of a resistor and a capacitor. Changing the values of those components changes the amount of time it takes for the capacitor to discharge.

The current control is probably a resistor /transistor circuit where the transistor switches upon a certain current level to control the on/off. Changing that resistor controls the current level at which the transistor is switched.

If we had a schematic, we could probably figure out which components control the various items and calculate what new values you would need.

I really had to deep in the bowels of my memory for this one.

mgianzero

Hey guys --- thanks so much for replying to me and not thinking I'm too crazy. I guess I'm just in my learning mode right now.

So this is what I did. I found a company called "Digi Key" who sells all sorts of electronic parts to the public. So I plugged in some numbers and came up with this:
OMI-SS-112L - general purpose 10Amp, 12VDC relay (there are three of them)
C547C - BJT transistor (looks like there are two)
resistors - those are obvious and there are two)
diodes - there are 11 if I counted right but too small to read numbers

Then there are two devices I can't figure out:
1) white ceramic square in center standing on its side (IainM said maybe a power resistor) what's that do?
2) block plastic square on its side with hole thru center (says "SEP RS 604" on its side but no match) (IainM said maybe a power transistor) What's that do?


Thanks. This looks like a cool site. Has a schematic and PCB board editors which allow you to design and build your circuits. It seems to incorporate the Arduino UNO boards as part of the design process. Is the Arduino a good place to start learning this stuff or is it for doing much more complicated projects?


So with all these devices and pic of the PCB board, is there a way to simulate how a device like this would work using circuit simulator software? My feeling is, how difficult can a board that turns an hold-down switch to a one-touch operation be to make? Am I over my head?

Kika

Short answer, no, you are not in over your head.

With circuit simulators, you can exactly emulate what the circuit will do in software. I all, this looks like a pretty straightforward circuit.

phoneyman

I'm with Kika on this one. It looks like the mixture of time and load control the window motor operation. The two blue boxes on the sides are your switching relays to turn power on/off to the motors. The third blue box is is probably a timer relay, especially if it has a potentiometer or DIP switches on it/ under the plastic (unless the caps and resistors set the timing). A power resistor is simply a resistor that can take more power. The small resistors are usually rated for 1/6 to 1/2 watt, that big white line can take more juice without frying. With all the diodes the board must also sense current request.

If you can't find every part number on digikey, try Fry's electronics, RadioShack and alliedelec.com websites to search serial numbers. I'd love to make this circuit for my car as a fun DIY in the future. Good luck

mgianzero

Okay. Does anyone have any familiarity with simulation software that can emulate something like this? There seems to be quite a bit of software development for designing boards out there. Some even run in a browser so you're up-and-running in no time. I just have very limited knowledge in what software to look for as I have limited understanding of all the devices used in circuitry.

If anyone is interested in "playing around" with this, I say we try to reproduce this board.

Then I have another application which I hope can be done with a modified version of this board and apply it for use for the all-electric rooftops on our 993 targas and sunroofs. It would, not only modernize our tops for one-touch operation, but incorporate a safety device that would detect high motor load and stop the mechanism before a potential jam (or body part) interferes with the mechanism.

I also have other devices I'd be interested in designing and building for our cars. But I think I should stop fantasizing too much and learn this circuit first.

Kika

Years ago we used to use SPICE, I don't know if that is still the SW of choice or if there is something more industry standard, but it may be a good start.
Then copy the circuit you have and understand what it is doing, the you can change component values to see what effect it has.

There are a lot of diodes in the circuit, so those may be the current sensing mechanism, not really sure.

The round components at the bottom of the first picture are capacitors.

phoneyman

I like circuitlab.com, pretty sure that's the url. It's a free browser based electronics layout program. OP is the best person to lay out the board since you physically have it. It'll be easier to layout the traces direct from the board. If I can get my laptop actually running before my new one shows up I'll work on it from the pictures for fun. Could you take a couple more pics of the top, from the four sides, like isometric angle shots?

mgianzero

Okay guys ... here are some pics of the circuit board, this time with backlight so as to show the circuit thru the top. All of the small black devices appear to be diodes (2 upper left, 3 upper right, 2 lower left, 3 lower right), except for the two BJT transistors in the center left.

I also just heard back from the designer of this board. Here are some of his comments ...

"The window express unit is a very simple circuit with a direction latch and a current sensing stall circuit. That Is all it will do, it will operate any small motor in the direction it was running until the motor stalls and the current exceeds 8 amps."

4X4SCHE

1) If you can't identify these common electronic components, your chances of modifying this circuit or designing a similar one are zero. The white one is a power resistor and the black one is a bridge rectifier.
2) I don't care what software you have... it will be no use because you lack sufficient knowledge to use it.
3) For such a simple circuit (for a person with any basic competence), software is not needed or even useful.
4) You should be ashamed of yourself for attempting to rip off someone else's work by copying.

phoneyman

1) you'd be surprised how many simple things an idiot can make with electronics and google; I'm a testament to that.
2) the software will be a good teaching tool for someone trying to learn the basics of electronics, so I wouldn't deter him from trying
3) again the software will help him learn. Same statement as 2
4) agree with you there. Did not know beforehand that a third party offered this solution. But like you said it's such a simple circuit most people would probably create the same circuit for the given purpose