One touch button for the soft top

[LeaUK]

More design tips - don't forget to decouple the power rails to each IC with ceramic caps 10nF + 100nF (1 off each to be on the safe side) and allow significant decoupling on the i/p power rail too (10nF + 100nF ceramic + 47uF tant >30V or equiv).

There's so much electrical noise in automotive design!

Also, can you clarify the R1/C1 and R2/C2 purpose as I'm concerned that there is no discharge if this is part of a timing circuit.

Lea

[bobterry99]

Hi Lea. Is noise a concern since this is a digital circuit? I've added pull-up resistors to the inputs and a diode to discharge C3 -- this was a requirement, as you had noticed. Thanks. Regarding C1 and C2, they discharge satisfactorily though U2A and U3A.

The purpose of R1, C1 and R2, C2 is to require the button on the remote to be pressed and held for a few seconds. Otherewise, you could not use the remote to just lock or unlock the car without operating the top. Also, these R-Cs allow you to use the switch to pause an operation -- for example, if the top is opening, then bumping the switch forward would pause the motion. Without the R-Cs, in this example the top would not pause, instead it would reverse the opening and proceed to close. In the basic design I am posting below, the R-Cs are not included and there is no pause.

I posted this on another forum:

The circuit attached is the basic circuit that does not operate with a remote. It is what I would choose to have for one of my cars. Cost is less than $2 for the electrical components and about $2 for a small board to assemble them on.

I have tested the circuit in my friend's '90 300SL and am satisfied that it works. The only anomaly I noticed was that if the car battery is disconnected and then reconnected, the top will automatically close immediately. I have a circuit modification to prevent this that will be incorporated into the design for operation with a remote. Without that mod, if you don't want the top to cycle when you reconnect the battery you can pull back on the top switch and cancel the action.

This circuit is essentially a simpler version of the others I have posted. The new schematic shows the connections at the top switch. Both the switch and its connector have pins that are clearly labeled 1-5 and 7 (they skipped 6).

If you want the ability to pause the top mid-cycle by momentarily touching the top switch, you can add a pair of resistors and capacitors. These were shown in an earlier schematic. Anyone who wants this feature can contact me for that simple modification.

The value of R3 and C3 set the time that the windows are rolled-up at the end of the cycle. If you have an older car with slow windows, you will want to increase one of these values. I'd suggest an R3 of 2.2K or a C3 of 1000uF.

If you decide to construct this circuit for yourself, there is a modification to your wiring that is not shown. Socket #2 of the connector is +12VDC that is switched-on with the key (Mercedes calls this "circuit 15"). But you need the top to work with the key off, of course, so you will need to bring unswitched 12-volts to this socket #2 (Mercedes calls this "circuit 30"). There are a number of places around the car where this can be done. If anyone needs assistance with that, then contact me.

One other point that was mentioned in an earlier post. I think the parts are available from M-B inexpensively to create a little harness with a male and female plugs that would allow you to just plug the new circuit in without cutting or splicing any of the existing wiring. I'll be looking into this.

Tomorrow I'm going to begin testing of the circuit for operation with a 1-button style remote.

[pigzmickey]

Guys, I guess thats it. I won't be bothering to promote these modules via this forum anymore, I don't make enough from them to afford forum tax..................................................................................................... ....
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[Strife]

Originally Posted by bobterry99

I expect to have the parts to build a prototype in a few days. I still need to work-out the resistor and capacitor values. If you or anyone else has some suggestions for improvements, I would much welcome them.

Your part selection is showing your age (and this is coming from someone probably your age, haha . If you use a microcontroller, you get all sorts of extra capabilities. The delay you have in mind could be done with a crystal controlled micro with great accuracy (use of RC networks in a car with the vagaries of temperature and humidity is treacherous, caps poop out, and crystals like the common 3.57 mhz are cheaper than dirt now).

Development systems with debuggers are very inexpensive now, I did my first gear start with a PC and about $120 of tools. One of my pet peeves with micros, an absolute invulnerable reset upon power up or glich (an absolute requirement with a product such as this), can be implement with solutions ranging from the cost of a resistor to about a buck.

[LeaUK]

I think we all agree that this project needs a uC (PIC 16F for example) and could be coded in a couple of hours, however this would mean increased expense as you would need to either 'purchase' the programmed uC or purchase a uC programmer - assuming the code was available.

I'm not one for rigorous cost cutting and so my preference and experience dictates a micro for but that's not to everyone's taste or natural ability so we'll see how BT99 progresses - with eager interest.

Just to ensure admin are not confused over this thread's evolved structure and to reiterate, with regards to BT99s proposed design this is purely investigative and nothing is being sold . It's all free! This is a community of R129 owners with some of us enjoying the technical challenge of repair, design and construction so I hope it will remain.

Just to add a few design tips to Strife's and those I previously mentioned on another forum included:


1. Please show decoupling so we can advise

2. Avoid relying on unknown impedances to assist with timing

3. Use controlled methods to achieve accurate and repeatable timing ie. a 555 would be a significant improvement - but it's not a great selection!

4. Use ceramic decoupling (10nF + 100nF) for each IC

5. Don't forget power supply i/p decoupling - 10nF + 100nF + 47uF Tant >=30V (or equiv)

6. Avoid slow ramping signals into gates unless the gates have schmitt i/p

7. Use schmitts on ALL i/ps and buffers on all external o/ps (I use schmitts for o/p too)

8. Apply signal conditioning to all i/ps - ie overvoltage protection etc



Enjoy...

Lea

[bobterry99]

Originally Posted by Strife

Your part selection is showing your age (and this is coming from someone probably your age, haha . If you use a microcontroller, you get all sorts of extra capabilities. The delay you have in mind could be done with a crystal controlled micro with great accuracy (use of RC networks in a car with the vagaries of temperature and humidity is treacherous, caps poop out, and crystals like the common 3.57 mhz are cheaper than dirt now).

Development systems with debuggers are very inexpensive now, I did my first gear start with a PC and about $120 of tools. One of my pet peeves with micros, an absolute invulnerable reset upon power up or glich (an absolute requirement with a product such as this), can be implement with solutions ranging from the cost of a resistor to about a buck.

Ironically, I program logic controllers for a living! But using software was not an option for this design. This is a forum for DIY advice, and the practical goal of my design had to be to offer a DIY alternative to buying an expensive module from someone else. Therefore, the design had to be restricted to inexpensive parts (preferably available at any Radio Shack store) that anyone with soldering experience could put together themselves. If my design used a microcontroller, I would have to sell these to people and that would put me in direct competition with Pigzmickey -- something I had no wish to do.

Anyway, the current vey simple design is working perfectly, so I'm not motivated to change anything at the moment, though I will be dusting-off an old textbook and looking at some of the points made by Lea. There is a time-constant in the circuit, but its accuracy is not critical. Technically, the nicest way to end the top closing cycle would be to sense the current to the window lift motors -- this would give a positive determination that all was done and would eliminate the R-C time constant.

[LeaUK]

Now current sensing is a nice idea Bob - just shame about having to splice yet another component/cable in to an adjacent circuit and feed to the centre console.

The electronics holy bible is of course 'The Art of Electronics' http://www.amazon.com/gp/product/0521370957/qid=1148279175/sr=2-1/ref=pd_bbs_b_2_1/103-2964385-8276609?s=books&v=glance&n=283155

[stats007]

Now on eBay