Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

need help with circuit design.

Status
Not open for further replies.

ccstech

New Member
I am fairly new to building custom circuits and need some ideas on how to make this system work. I am familiar with relays, transistors, diodes, resistors, and such. I am also able to solder and have some project circuit boards. I have a 2.5volt source that comes on and off at 2-3 second intervals for 5-6times when triggered, I need it to send just one ground pulse that can handle 1.5 amps at 12volt for just a few seconds.(like triggering door locks in a car) Im hoping to be able to build this with inexpensive parts that I can get easily. The exact use is im using the feed wire off a cell phones vibration motor to activate the accessory wire from remote car starters. When you text the phone it sends 2.5v 2 times and when you call it sends 2.5v 5-7 times. I need a circuit that on the first 2.5volt will send a ground pulse to the specified wire and also cut the input feed for 60 seconds or so to ignore other pulses. Any ideas would help out greatly.
 
What's a "ground pulse"? We need a little better idea of what you're trying to do here (like pulse polarity, voltage, duration, current, like that).
 
[QUOTE="ccstech, post: 1202984, member: 255387" I have a 2.5volt source that comes on and off at 2-3 second intervals for 5-6times when triggered, I need it to send just one ground pulse that can handle 1.5 amps at 12volt for just a few seconds.(like triggering door locks in a car) Im hoping to be able to build this with inexpensive parts that I can get easily. The exact use is im using the feed wire off a cell phones vibration motor to activate the accessory wire from remote car starters. When you text the phone it sends 2.5v 2 times and when you call it sends 2.5v 5-7 times. I need a circuit that on the first 2.5volt will send a ground pulse to the specified wire and also cut the input feed for 60 seconds or so to ignore other pulses. Any ideas would help out greatly.[/QUOTE]

Is the phone powered by battery or charger. I have a concern that if the phone is being charged the 2.5 volt signal may not be near ground. So maybe the input needs to be isolated so we don't have a ground loop problem.

I am assuming the output needs to pull down to ground for 2 seconds.
There needs to be a 60 second timer.

Are you building one or thousands?
 
Sorry if it wasn't clear enough the draw is max 1.5amps at 12volts for 1-2 seconds on negative feed side. The source trigger is 2.5volts. Our remote starts have an accessory start wire that when you ground it for a second it starts the car, this wire can be hooked to door locks to be able to start the car from factory remotes when you unlock/lock doors or from other aftermarket devices, it just needs a "negative ground pulse" wording per manufacturer of units.
 
The phone will be powered by charger most all times. Once I master it and get a stable working unit ill build them as customers want a cheap cell powered unit. We currently have a system we install that has its own "gsm relay" but its $250 extra dollars and I believe I can build the same using a $10 prepaid cell phone. We are small outfit so im thinking we would pry build 25-50 units over a couple years until the cool wears off.
 
A small 8 pin micro controller could easy do the logic for this job.
A 60 second timer is easy in software but add parts in hardware. I feel you can't do software.

The transistor/relay/MOSFET that does the 1.5A 12V switch is simple.

I am thinking on which is better (hardware or software).
 
Sounds like you need 2 monostables - you could build these from discreet transistors or use in IC (I'm sure there are some on the 74 & 4000 logic families, but I don't know the numbers off the top of my head). One with a short time-constant to trigger the starter, and one with a long time-constant to inhibit the first from re-triggering.
That said, I'm inclined to agree with ronsimpson, that a micro would probably be the better option - building long (several minute) time-constant RC timers to work reliably in an automotive environment could be tricky. A micro will be more repeatable and easier to tune.
You'll probably want to build some kind of filter/peak detector to pick up the ring signal from the 'phone, and use a MOSFET and relay to drive the starter (a relay will help isolate your circuit from any electrical nasties floating around the car's electrics).
 
If that was the case i would just hook the drive motor to a transistor and then to the ignition feed when it rang boom!! who cares after that.. Thanks for the ones trying to help out. Anyone have any schematics for a similar setup or could take a few minutes to draw one up.. Thanks
 
actually that wouldn't be enough power you'd need some kind of spark gap arrangement ... like in a car ignition as you describe ...

Anyway I was just pointing it out, gotta be carful on the internet, especially when a new unknown member starts makes slightly strange requests with no explanation of the end application
 
especially when a new unknown member starts makes slightly strange requests with no explanation of the end application
Just like at least 50% of the "first posts" here.
Business as usual, now back to sleep.:)

JimB
 
And why would you use a phone? An RF transceiver would be far more sensible. I mean who wants to start their car from miles away.

Sorry but you're really going to have to help me out in understanding what you're trying to do here
 
Have you considered that anyone dialling a 'wrong number' could activate the starter by mistake? Sounds dangerous to me :eek:.
 
In 2014 we sold 27 gsm controlled relay remote starts installs. The basic unit is $199 for the remote start and an extra$250 for the ability to start from cell.. Can a wrong number start your car? Yes but if you unlock the doors, hit the brake, rev the engine, open hood or put in gear will shut the engine off, also the system only runs for 5-10-15min programable then shuts down anyway, so a wrong number Is not a big deal. Its no different than setting on the RF key fob that also can start the car. Rf even long range units usually cant start your car from inside the mall when its the middle of winter here in Michigan. So yes a cheaper solution here is a prepaid cell phone as a trigger for the remote starts we already install the systems anyway. If I can offer a unit for $99-$159 many more of our customers would add the feature. Also if the customer is worried about the wrong number problem we can simply program the remote start to lock doors when the car starts this feature is on all units we install, then set the phone to a standard ring tone with no vibration low volume and then turn on distinctive ring tone and set it to vibrate on what ever number you would call from standard features on most phones.. AS far as "strange strange requests with no explanation of the end application" I put exactly what My needs were in the original post..
Again thanks for helping.
 
Last edited:
I did a project a few years ago to control an oil pump on snowmobiles equipped with a turbo. I think with a small change to the hardware (add the opto isolation on the input) and tweak the software you would be up and running.
 
Here's a simple circuit that I think you were after. I marked it as using 12V, but you can use a lower voltage instead, within reason, if you wished. You will need to make sure the 12V supply doesn't have any spikes or surges that could damage the circuit.

Each incoming pulse causes the first RC timer to start, which stops retriggering for ~6 seconds since the last pulse. On only the first pulse, the second RC timer is started, which outputs a ~1.3 second pulse to the MOSFET at the output. You can increase that period by increasing the resistor and/or capacitor value.
timer.jpg
 
Dougy, Why all the NAND gates??

All you need is a level shifter, a monostable and an output drive circuit.


However personally I think a better solution would be an Arduino with a GSM shield. You could always add a password or limited accepted phone numbers
 
Dougy, Why all the NAND gates??
One is used for each timer, and then there's an inverter to drive the FET at the right time. There's 4 in a package. Could use a hex schmitt-trigger inverter instead, or two 555 timers to a similar effect.
All you need is a level shifter, a monostable and an output drive circuit.
Please draw it up and post.
 
A small 8 pin micro controller could easy do the logic for this job.
A 60 second timer is easy in software but add parts in hardware. I feel you can't do software.

The transistor/relay/MOSFET that does the 1.5A 12V switch is simple.

I am thinking on which is better (hardware or software).

I tend to agree with using a micro-controller for this application and here is why. The original poster plans to make several of these things, let's say 50 or so. I can buy a simple 8 pin Picaxe 08M2 uC for about three bucks a copy. Any number of cheap off the shelf boards would accommodate the things. While I am far from being a programmer type the level of programming needed is about a minus 3 on a scale of 1 to 10. :) Even I could do it. The required programming software is all free. So for making several units I would take the micro controller and software route. Once the simple program is written you just program your 50 or so chips and that is about it. I guess if you wanted you could have 50 or so custom boards made relatively inexpensive.

If this was a project for one or two units I may go the discrete component route but it just seems to me for what the original poster wants a simple 8 pin micro controller is a logical choice with some very simple code. I also liked Dougy's solution but for this would go the uC route.

This also all assumes the original poster is not concerned with dialing a wrong number as was mentioned. Just coming off a cheap cell phone into the start system.

Just My Thoughts
Ron
 
ReloadRon points to a good choice. With your low volumes you need to have low design effort.

PIC10F220T-I is a 6 pin micro for 50 cents at 1 and 30 cents at volume. It will take more effort to get it running.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top