Seeking help with a circuit design

Topic: Seeking help with a circuit design (Read 4064 times) previous topic - next topic

Seeking help with a circuit design

Reply #15 – June 16, 2012, 10:13:20 PM

I still perfer stamp and pic controllers. My dad programmed his adruno (sp?) To run sequental turn signals, among other things.

Seeking help with a circuit design

Reply #16 – June 17, 2012, 10:34:24 AM

Quote from: TOM Renzo;392381

Could you use a headlight timeout module. Or a dome light module that delays. Just saying.

Awhile back I built this circuit in order to keep my cooling fan running for a delayed amount of time after I shut off the engine, using a 555 timer. Worked pretty well but had a few bugs (features). To build a robust circuit for automotive specs it takes more than a simple R and C. Diodes and caps are needed to protect the timer output and dampen spikes. One 'feature' my delay had was when I hit the door locks, there was spike that triggered the timer and started it running again. I was bummed at first then decided I liked the 'feature' to manually turn on the fan again. (I should have worked for MSoft :hick:)

One concern I had was the specs of the Radio Shack components I was using. Not sure if they were designed to handle the temp/voltage in an auto application. Think about how hot your car gets during the day and check the specs of some components.

There is a website that has simple 555 timer circuits where you can plug in the delay desired and it will give you the R and C. If you search 555 timer you should be able to find it. But again, in an automotive application it's a bit more complicated then a simple lab bench circuit.

Quote from: TOM Renzo;392381

Could you use a headlight timeout module. Or a dome light module that delays. Just saying.

I wanted to go this route using the latest parts from a junkyard car but didn't know what to look for and if I found it, the details and pin-out.

I'm still interested in a design to replace my current 555 design so if someone comes up with something feel free to share it here.

Seeking help with a circuit design

Reply #17 – June 17, 2012, 10:03:06 PM

I found a java applet that's proving to be very handy, and I've got everything working in the simulator, but I can't figure out how to interrupt the 555 with the door ajar signal, and have the timer NOT continue when I take the signal away.

Seeking help with a circuit design

Reply #18 – June 17, 2012, 11:23:10 PM

I think I got it. Now I have to work out the finer details, including component specs, and a parts list. Anyone interested in my circuit for the hell of it, or for verification, can find the simulator I used here: http://www.falstad.com/circuit/
click: File, Import, and paste the data from the .txt file in the box, then click the Import button. You can start the sim by clicking the switch labeled IGN SW, which will power up the 555's trigger and the Accessory Delay relay. Once you click again to turn off the ignition feed and kill the trigger signal, the 555 responds by feeding the Accessory delay relay's trigger terminal, and keeping it on for 10 minutes (30 seconds in the sim, so as not to offend my ADD), or until you simulate a door opening by clicking the switch labeled DOOR AJAR SW, which is a momentary contact to ground (momentary is in order to verify that no minimum door open time is required) which grounds a npn transistor, cutting the reset feed AND the source to the 555. Anybody who has ACTUALLY worked with this stuff before should let me know if I'm on the right track. Thanks.

Seeking help with a circuit design

Reply #19 – June 18, 2012, 03:22:13 AM

I wouldnt choose that method because in some cases simple is just better, but hey, if you can walk away with something you learned then thats great.
The actual size Cap and Resistor for your application might be roots of 8 so an 800kohm resister and an 800uF cap would be more applicable to 10min or 640sec.
Parts
relay
Variable Resistor (or 800kohm), (color band should be GREEN,BLACK,BLACK, Orange if set value resistor is chosen)
Variable Capacitor or just a standard one as shown (800uF)
Door Jam switch (open with door closed like your OEM)
Door Jam switch (closed with your door closed)
optional amring switch

Condition 1 as shown "door closed"
-Manual switch 1 (ms1) is closed , consider this optional "arming" switch.
-your door is closed, ACC is selected and desired load is on via the relay
-S1 has continuity and is mounted in your door jam (works opposite of OEM switch)
-Relay coil obtains ground through the series RC circuit to ground
-at approx 10min the capacitor will reach stead state and the circuit is open.
-The relay will de-energize because the 10min interval has been met.
-S2 is open (same type of switch as your oem door jam switch)

Condition 2 as shown "door open"
-MS1 is closed (again an optional "arming" switch)
-ACC is still selected and desired load still on from previous condition via the relay.
-your door is open
-S1 door jam switch opens (again opposite from your oem door jam switch)
-Relay will de-energize if less than 10min have passed due to RC circuit and you desired load on the relay will power down
-S2 closes and discharges the capacitor so it can reset itself for a new cycle

---capacitors (sorta like a battery) act like wires during thier *initial* charge up so they conduct like one initially.
They will eventually match the source voltage and the difference in potential will be null, the cap will fully charge and prevent current flow at the specified combination of resistive and capacitive combinations.

Seeking help with a circuit design

Reply #20 – June 18, 2012, 03:50:20 AM

Quote from: rodsterh;392551

To build a robust circuit for automotive specs it takes more than a simple R and C. Diodes and caps are needed to protect the timer output and dampen spikes.

A little advice, keep it simple when at all possible. Only swag in a digital or buttstuffog input to ADIO devices when all else fails and your forced into TTL logic cirucits. They work like a charm but sounds like your problem was planning out the total circuit insuring there was complete circuit isolation on the retrofit you did. Your power sounded dirty or a momentary backfeed from an obscure source.

We made it to the moon with simple circuits and tubes, this isnt rocket science. Your saying it can not be done but yet its happening all around you and was the first time delay system for wipers, still basically is in our cars so why it can not be done is a mysterious statement.

Seeking help with a circuit design

Reply #21 – June 21, 2012, 01:46:08 AM

sorry i forgot to mention this, didnt want to get too deep into the high level details but here it is.

your total resistance with the resistor plus the ohm value of the relay coil must equate to around 800kohms. ITs hard to predict what the relay coil will be as it depends on which one you choose. Some relays coils have blocking diodes and if you read approx .3 to .6 ohms one way then flip your leads and have like 200kohms the other way, then you have a blocking diode. This is relevant because timing is everythign. this is why i suggested a variable resistor so you can dial it it.

Seeking help with a circuit design

Reply #22 – June 21, 2012, 08:00:43 AM

I used an extra relay because diodes weren't giving me what I wanted. I have some 15 amp PCB relays in my tool box, I'll use one of those for the isolation relay, and I'll use a plain 1x1 relay externally for the actual accessory delay relay. I could use an 800k R, I'll just have to go back to the 555 calculator to get a new value for the Cap. The control Cap has to stay at 10nF. I need to use a transistor for the door ajar signal switching, because it's easier to work into the circuit with the way the vehicle is set up, and because I don't really have any current to speak of on the reset pin. The transistor kills the reset pin, the Acc Dly drops and cuts the output AND drops the Vcc power, which was a big deal to figure out when I was working out the diagram. You wouldn't believe how long it took me to realize that if I didn't want the 555 to keep counting when I cut the reset, I'd have to kill the Vcc power, too. I'll probably try to start building next week, once I talk to another guy I know about what voltage values the caps need to be, what the specs on the output diode need to be and what I'll need for the transistor,

Seeking help with a circuit design

Reply #23 – June 23, 2012, 11:31:04 PM

If 10 mins is too long for a 555, what about using a 556 and chaining the two timers?

Seeking help with a circuit design

Reply #24 – June 23, 2012, 11:41:49 PM

I suppose an easy way to control when the circuit shuts off could be to drive a 555 at 1/60 Hz and have it drive a 4017 decade counter. When output 9 goes hi, 10 minutes have elapsed. Or if that frequency is still too low for the 555, chain two decade counters (output 9 of the first one supplying clock input to the second one) and drive the 555 at 1/6 Hz (pulse every 6 seconds).

Seeking help with a circuit design

Reply #25 – June 24, 2012, 11:10:42 AM

I went back and customized the sketch i had lying around for another application to suit yours, i thought you would figure it out.
The RC formula is T=RxC ,,,,, t=time, R=resistance, C=capcitance

T= 800000ohms x .0005farads , = 640seconds, which divided by 60sec = 10.667 min delay.

You just have to make sure the resistivity of the relay coil + the resistor fall somewhere in the 80kohm range,, again a variable resistor.

Not sue what needs your design has that are not capable of being controlled by the RC circuit, did your needs change from you original post? If not, you dont need the headache your experiencing (told you so : ) ) by over complicating this.

You should consider powering the design off your existing platform voltage source which is 12v and this does the trick.

anything beyond that and i would be suggesting a quad NAND gate for logic highs and lows with a user supplied 5v isolated source. 5v does exist on your dash by the way.... if its not dirty which it likely is as there is plenty of AC harmonics on our alternators.

I went back and corrected my post and drawing for this specific application, btw, 500nF caps arent really a common choice in the wattage range your application would box into.

Good luck and have fun, and if all else fails, fall back to simplicty and try out the rc time constant option you have now, you wont need the 555 timer anymore.

Seeking help with a circuit design

Reply #26 – June 24, 2012, 11:22:28 AM

oh yeah,forgot to add,

when I build or design something, i have to consider risk on what we call "SPOF"
You should consider reducing "single points of failure" when too many parts are integrated into a design.

as i said before, keep it simple with long lasting results, thats the end game at the end of the day.

Seeking help with a circuit design

Reply #27 – June 24, 2012, 11:41:10 AM

Actually, I got it. I had my prototype working yesterday. I ran it at 30 seconds for verification, then, since I'm using a breadboard, I swapped the resistor and ran it just a couple tics past 10 minutes. Also, the npn transistor kill switch works awesome. I can't wait to get it on some project board, and into a small project box. I may build another with a surface mount 555 on a sparkfun dip14 breakout board, so that I can build the whole thing on the small breakout, and then mount the acc delay reay externally. Before you reply that a 555 is 8 pins, I'd use a breakout with extra pins so that I can use the extra pins for mounting the components.

Seeking help with a circuit design

Reply #28 – July 10, 2012, 11:58:47 AM

I built an on-board prototype last week with relays for kill and isolation, and yesterday I completed what I've decided is my finished product with transistors for isolation and kill and only a 4 pin 60A relay for the Accessory Delay. I think the second looks nicer and works more quietly. I've only run them on the bench so far, but they both work. Maybe later in the week I'll get one installed. I've noticed (happily) that everything I want to run with it is all on the same output from the ignition switch (radio, windows, clock, courtesy lamps, and moonroof), and that I'll be cutting down the current running through the switch by at least half. Less current through our ignition switches is a very good thing. Sorry for such large pics, but some guys will want a detailed look at it.

Seeking help with a circuit design

Reply #29 – July 10, 2012, 12:44:08 PM

Special thanks to Thunder Chicken, your idea got me going in the right direction, and to jcassity, even though I didn't go with your simple version, it was very helpful to have somebody explain the finer points to me. My final RC values were 549k ohms and 1000uF with a 10nF as the constant and 2.2k ohms between kill trigger and kill power to make the transistor act like a nc relay. Somebody asked for a diagram when I figured it out, so here it is.