Help with simple controller project

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codmfer

Joined Apr 14, 2013
8
Hi I'm looking to use a microcontroller that will, when powered up by a 12v switch, put out 2 ground pulses on the same output about a half second to a second apart. The timing is not really important. Then I want it to stay at ground on the second pulse. Then when powered down will reset and dothe same thing on every startup. Ive had a couple classes involving microcontrollers but never really did much with them. Ive been looking at different controllers but im just not sure where to start. Any help is greatly appreciated.
 

Thread Starter

codmfer

Joined Apr 14, 2013
8
Ok thanks for the input, I was looking at the 555 timers since ive actually had some experience with those and i see how to create the pulses with it but i dont know how to make it stay at ground after only two pulses. I am very amateur at this. Im thinking a monostable oscilator is kind of what im looking for. Correct me if im wrong
 

LDC3

Joined Apr 27, 2013
924
Let's clarify your needs.
Before the trigger, you want a high output signal.
At the trigger, you want the output to go low (for 250ms to 500ms), followed by a high (for 250ms to 500ms) and then a low (until trigger is released).
 

Thread Starter

codmfer

Joined Apr 14, 2013
8
You are right for the most part. But i would actually like for the 12v trigger to not only be the trigger but i want to use it for the supply voltage too. The output does not actually have to put out any voltage at any point as long as there are two ground pulses and a latch on the 2nd pulse. Then want it to do the same thing every time the trigger comes on.
 

LDC3

Joined Apr 27, 2013
924
You are right for the most part. But i would actually like for the 12v trigger to not only be the trigger but i want to use it for the supply voltage too. The output does not actually have to put out any voltage at any point as long as there are two ground pulses and a latch on the 2nd pulse. Then want it to do the same thing every time the trigger comes on.
It will be difficult to have a high signal when there is no power in the circuit. It will be much simpler only to use the trigger as a signal, instead of powering the circuit.
Also, I'm not certain what you mean when you say it doesn't require any voltage. Do you mean to activate an open drain?
 

Thread Starter

codmfer

Joined Apr 14, 2013
8
What im saying is i dont need the circuit to be high on the output at all. all i need here is 2 ground pulses with a latch on the second ground. The reason i want to use the trigger for the supply too is so i can only have 3 wires coming off of the board for me to hook up. I dont guess it would be a big deal to use another source for the power but i would just really rather not. So ideally i just want power(trigger wire), ground, and the output which will put out 2 pulses of ground about a half second apart and stay at ground on the second pulse until the circuit is powered off.
 

Thread Starter

codmfer

Joined Apr 14, 2013
8
I dont have an exact answer for that but it is basically for ground detection. This ground will not be actually powering a circuit if that makes any sense.
 

tracecom

Joined Apr 16, 2010
3,944
Ground must referenced to some voltage. What is that voltage and how much current will flow?

Better yet, what are you trying to do?
 

Thread Starter

codmfer

Joined Apr 14, 2013
8
haha I had no idea this would create so much confusion. Let me try to explain this better. Lets say I have a 12 volt trigger wire that comes on and off with the turn of a key. This wire is usually a 1-2 amp max current wire. I want a small device that will turn on with that wire and send 2 half second long pulses of ground about a second apart and stay at ground on the second pulse until the trigger wire is turned off. The device will be grounded to the chassis of a car which is connected to the ground of a 12 volt car battery. The output of this device is sending a double pulse ground to a parking brake detection wire which requires very little "ground strength.
 

ErnieM

Joined Apr 24, 2011
8,130
What im saying is i dont need the circuit to be high on the output at all. all i need here is 2 ground pulses with a latch on the second ground. The reason i want to use the trigger for the supply too is so i can only have 3 wires coming off of the board for me to hook up. I dont guess it would be a big deal to use another source for the power but i would just really rather not. So ideally i just want power(trigger wire), ground, and the output which will put out 2 pulses of ground about a half second apart and stay at ground on the second pulse until the circuit is powered off.

OK, 3 wires: return, 12V signal/power pulse, and switch to ground.

Not impossible. Not very complicated either as the power/signal exists for the entire time the output is active.

Two 555's could do it, one triggers the other to get the initial pulse-pulse, something to combine the signals, and whatever switch element you use. Transistors, MOSFETs, even a relay are all possibilities depending on your load.

Of course any micro controller with 4 or more pins (power, ground, 2 I/O's) could control the switch element directly. That included the PIC10's and all their 8 pin micros. I'm fond of the PIC12HV615 that has an internal shunt regulator so it can regulate it's own 5V supply off the 12 V: saves a part or two there.

(Side note: the case for a "short signal" is not defined.)
 

Wendy

Joined Mar 24, 2008
22,360
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