One for the electronics guru's

[BradW]

Just check the draw current of the relay. The 2N3906 transistor is only good for 100mA. Also, why is the first pulse on for 1.3s, and the second pulse on for about 0.7 seconds?? What is the on time in steady state?? Im just concerned that the circuit might leave the wipers in odd positions. What happens when the car is switched off halfway through an on cycle?? does it head back to zero when the car is switched back on??

Im thinking there is a relay inside the motor which switches itself off when it returns to the normal position(wipers down), and holds on when not in the normal position, because the wipers always return to the normal position when you switch the car off, and the turn it back on with the wiper switch off. They also return to normal position when you switch the wipers off with the car running. Perhaps the circuit need only run for half a second each cycle, and just adjust the frequency of operation. I think we all need to look closer at the original wiper design, as there should be features there we can use to make the circuitry simpler.

Cheers, Owen

The wiper actually has it's own internal switching which "self parks" the wipers (ie returns them to the bottom of the screen when switched off.
The intermittent wiper module needs only to move the wiper arms a short part of the sweep for the self park to take over and finish the sweep. This is why care should be taken when working on or around the wiper system (arms, linkages and motor) with the ignition on as the self park circuit can be engaged by moving the wiper arms (if possible) and body parts can get caught up in the linkages .
So the on time of the intermittent wiper output needs only be 1-2 seconds (depending on the wiper motor). Enough to move the wiper motor into self park mode which continues the sweep.
The on time will trigger the sweep and the off time will determine the amount of time between sweeps.

i have always liked the idea of "pic'n" my car. and i have done a few things in my time with the car as well, the next progect5 i am looking at is running a 40x2 LCD off at ATMEGA8 just to tell me stuff like batt voltage and other useful things.

Anyway i have been really busy but just threw this together. the idea of using R# in your circuit Brad is ok but i prefer using as little components as possible . And since we are using a MOSFET or BJT (transistor) if we make it an inverting circuit then we can dispose of the third resistor. I prefer BJT's because i can get them to do exactly what i want (i always have to have a play with MOSFETS to get them to work...

Anyway here you go, i have played with the values to get my software to work, sorry i didn't use actual E24 series so these exact values don't exsist but hey, you get the idea. the RL is the load so the relay or anything. This circuit will work wired from the exisiting switch and assuming there is already a relay to the motor you may just be able to use a decent transistor instead of an extra relay. Anyway we will see how mods to this work.

Oh and below the circuit diag is the simulation of the circuit. the output of the 555 is actually the opposite (long high time, short low time) and then the transistor (PNP) inverts the signal..

Firstly what is a "pic"?

Thanks for the circuit. No need to apologize for not using "E24 series" as I have no idea what it is .

I don't really understand how that circuit works so I'm off to do more googling.

Everyones input is appreciated greatly, Rep points all round .

[myne]

I'm fairly certain the ae82 intermittent works like this :

Transistor switches on, charges a capacitor, when the capacitor is charged, a small relay turns on. Relay works wipers and turns transistor off. Capacitor slowly discharges, relay turns off, transistor switches on. rinse, repeat.

[o_man_ra23]

A pic is a simple and common microprocessor. A very simplified version of a computer CPU if you would like. Often you will find things like pics inside ECU's and the more complex of the spark controllers. Another microprocessor commonly used, but now outdated is the motorolla MC68HC11... ive done quite a bit of work with these, and they are quite a powerful processor when their features are utilised fully. The HC11 can be found in ECU's such as the injec EM1/2/3, and im sure many others. Pic processor range in price from a couple of bux to 50 or so dollars depending on the complexity of the processor and its abilities. A pic programmer is available from jaycar in kit form for not much, but a pic in circuit debugger will set you back about $250. This is still a lot more affordable than the kits for other processors, making the pic quite popular with enthusiasts.

Myne... later model wipers probably do work off a transistor/capacitor network, ill have to pull apart an RA40 wiper motor I have and check out how it works.

Brad, very sound advice on the safety of working with wiper motors, rep for you

Cheers, Owen

[ndgcpr]

Just check the draw current of the relay. The 2N3906 transistor is only good for 100mA. Also, why is the first pulse on for 1.3s, and the second pulse on for about 0.7 seconds?? What is the on time in steady state??

The first pulse is 1.3 and evey other one is 0.7 secs. it just takes a bit to initiate. I was looking for around .5 seconds because i was assuming it was a self returning wirper. This also means that this circuit can go in between the "pulse" section of the wiper like so



Worst comes to worst i am more then happy to build this for you, with the weight i would think it would be no more then a couple of bucks to mail it anywhere in Australia.

[o_man_ra23]

Should work a charm, but i might look at using a pic anyways, and buy the programmer and in circuit debugger. But once again, check the draw current of the relay before using such a small transistor.

Cheers, Owen

[ndgcpr]

yeah the 2N3906 was the first one i had the specs for. but any PNP should be a straight swap.

Oh and for the question a while back the E24 series is resistors, there are a few series. the most popular is the E12 and E24. And as you would expect the E24 has 2ce that of the E12. they are just the types available in the shops.

Here is a link to explain it better.

http://www.logwell.com/tech/componen...or_values.html

The number after the E is the number of resistors between 0 and 1000. then they repeat as K and them there should be M i think. so if there is a 47ohm resistor, there will be a 47K and 47M.


Also o_man_ra23

Look into ATMEGA's (atmel microprocessor) the devleopment board (STK500) is really good and i like them, they are basically a bigger PIC. i have a PIC programmer and am now looking at getting a ATMEL board cause i use them more.

[MWP]

If you dont need the power of a ATMega, look at the AVR 8535 and 8515.
They are great for small-medium projects and are availiable everywhere (Jaycar for example).

[BradW]

Oh and for the question a while back the E24 series is resistors, there are a few series. the most popular is the E12 and E24. And as you would expect the E24 has 2ce that of the E12. they are just the types available in the shops.

Here is a link to explain it better.

http://www.logwell.com/tech/componen...or_values.html

The number after the E is the number of resistors between 0 and 1000. then they repeat as K and them there should be M i think. so if there is a 47ohm resistor, there will be a 47K and 47M.

I have actually read that somewhere so I should have known what you meant .
Once again a big thankyou to all for your input.

[Cool1]

Should work a charm, but i might look at using a pic anyways, and buy the programmer and in circuit debugger. But once again, check the draw current of the relay before using such a small transistor.

Cheers, Owen

Why would you want a "circuit debugger"? All of your circuit debugging should be be done in your design tool(Protel?) and all the code should be sorted in what ever you are using to assemble your code!

If you want to get into pics visit http://www.dontronics.com/
You'll find some nice development platforms there that will get you started

[o_man_ra23]

You would be amazed the crazy things that microprocessors can do in unforseen circumstances. Besides, anyone who has programmed in assembly should know that nothing ever works right the first time. Mostly cause assembly is so finniky and gets repetitively boring after the first 50 lines. Same with board design. Plus its great for seeking out shorts, dry solders and broken components, even after the board has been in service for some time. Just plug in and find out whats goin wrong No design should be put in service without extensive testing, as a failure on the road could mean anything from a copper pulling you over cause your indicators no longer work, to your life if the ABS fails, or your car if the power window gets stuck down. I would rather test and be sure than debug onscreen and have something fuck up.

Cheers, Owen

[camrygt?]

Hi
My dads morris minor has been using a 555 timer and a relay that we built for it at least 15 years ago. Sold the car now but wipers never missed a beat in all that time.

Use the NE555/LM555 not the CMOS one, they can drive more current and I have found them to be more rugged.
this link shows you how to drive a relay with a 555 and how to set up the diodes to stop the back emf (high voltages that blow up the chip when driving a coil)
http://www.jaycar.com.au/images_uploaded/relaydrv.pdf

This is the 555 data sheet which shows the output transistors built into the 555 can drive up to 200ma which at 14 volts means you will need to use a relay with a coil resistance higher than v=ir 14 = 0.2 * 70 ohms
http://www.jaycar.com.au/images_uploaded/LM555.PDF

disk smiths and jaycar still sell the 555 chips they cost $1 from jaycar

don''t bother with a mosfet they are great once working but unless you have lots of experience they can be difficult.

Also the 555 timer in astable mode (the circuit you have shown) normally has a 50% minimum duty cyle. You probably want something more like a 10% or less duty cycle so I would set the timer up with a 90 or so% duty cycle (Ie output of timer is HIGH for 90% of the time) and wire the relay up so so that the output of the 555 pulls the relay coil LOW to turn it on. Have a look at the relay driving link on the jaycar website, the pic at the very bottom is set up this way with the relay coil between power and the output of the 555.

let us know if you have any trouble

[o_man_ra23]

Why is everybody so afraid of MOSFETs for this application?? sure they take a bit of time to set up in an amplifier, but when running switchmode like you would with wipers, they are a peice of cake to setup. And they can switch much greater currents, require a smaller gate current, and have much less drain/source voltage. They arent that dear either.

Cheers, Owen

[Cool1]

You would be amazed the crazy things that microprocessors can do in unforseen circumstances. Besides, anyone who has programmed in assembly should know that nothing ever works right the first time. Mostly cause assembly is so finniky and gets repetitively boring after the first 50 lines. Same with board design. Plus its great for seeking out shorts, dry solders and broken components, even after the board has been in service for some time. Just plug in and find out whats goin wrong No design should be put in service without extensive testing, as a failure on the road could mean anything from a copper pulling you over cause your indicators no longer work, to your life if the ABS fails, or your car if the power window gets stuck down. I would rather test and be sure than debug onscreen and have something fuck up.

Cheers, Owen

Microprocessors dont do anything that you dont tell them to do!
I have programmed in assembly and its not that repetitive at all and if it is your doing something wrong. If you have something that needs to be inserted many times, you just simply copy and paste or simply include it.
Plus in the real world no one ever starts from scratch anyway. You always start with something that works and then simply add to it and most often by adding code that you have used in the past.
As for PCB design, it cost a few thousand dollars to tool up for a print and then once you print out 10000 or more PCBs you better hope you have no mistakes because its too late to change it.
In my company when we need a new product a circuit is drawn up by a group of people and then another group of people write the code. Once this is done the 2 groups get togeather and discuss how things will work and once they are happy all goes into production.
The circuit will be drawn into a PCB which will then go to whoever to print off a batch of at least 1000.
The code will then go to a micro manufacturer who will program the micros in production. Minumin buy is most often 10000.
Another group of people will now be called into design a case/housing for the new product.
More people will be contracted to design packaging.

And that there is how just about all manufacturers will go about business! Why? Because money talks!
I wont and no other company will employ some pussy who wants to waste time and money testing every step.

[camrygt?]

nothing against mosfets at all my car has at least 20, but for someone who hasn't used them before they can be difficult.
Ie the gate is generally static sensitve.
For most types if you put more than 10 volts across the gate they blow up.
Most have the metal tab at the top connected to one of the pins which needs to be insulated or kept out of the way
If you get a short on the output the mosfet is more likely to disintergrate before a fuse blows than a relay is.
And if not set up correctly the huge gate impedence can cause them to begin to turn on when you don't want them to by picking up induced voltages from ignition systems etc

Plus if driving a motor directly mosfets are not as rugged as they first appear, think about the inrush current when you first switch on a DC motor and have a look at the Safe Operating Area on a datasheet for even a 60 amp mosfet and you will see why it is much less complicated to just use a relay

Also the majority of people who are likely to work on a car know how to use a relay but have never heard of a mosfet so if something goes wrong at least someone can fix it if its kept simple, 99% of cars still use relays to switch indicators, wipers, fans etc for these reasons
cheers

[river]

Hi,

Most of my prototype microprocessor stuff is wire-wrapped. Some of the simple ones I do the design on paper, but more difficult and complex circuits I usually put onto Protel 99SE.

I have some AVR and PIC devices which I have played with a little bit, but being the old hack I am, I just love playing with my old 8080/85, 6800/02, 6809, Z80, 68000, 6502, 2650 and SC/MP systems. I program them all in assembler - the ultimate man's language - and write my own debug/monitor/operating systems.

Also I repair old Multibus, SS50, STD and S100 systems. All this stuff is in my blood and I just can't help fooling around with it.

Yes you are right, my froggy friend, that the processor will go spastic only if you program it to do something dumb. Sometimes though you can do something dumb like hook an address line to a data bus line and wonder WTF... but after a circuit check you realise your mistake.

I too have nothing against the wonderful MOSFET, but, in reality, to drive a simple relay requires just your ordinary junkbox trannie, and therefore leaving the MOSFETs for more important projects where their operation/specifications are truly required.

seeyuzz
river