Looking for a schematic for 1 pulse in, 2 pulse out

Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
Hi everyone,

I have an idea for a project for my car. I want to be able to use a Microwave motion sensor to trigger my under car LED lights on and off. The LED controller has one button for on and off. The same push button turns on and off the LEDs.

I would like to mount an old Alarm proximity sensor to my front bumper. When something passes near the front of the car. The prox sensor sends out a negative DC ground pulse to turn on the LEDs. Then after a few seconds, between 3 to 15 seconds variable. Another pulse is sent out to turn off the LEDs.

I plan on soldering across the LED controller power button to interface with this circuit I am asking for. I do NOT know where to start start building this circuit. Any input or direction is most appreciated.

Thank you
TONY
 

wayneh

Joined Sep 9, 2010
16,162
The LED controller has one button for on and off. The same push button turns on and off the LEDs.
It's quite likely that the switch closes a connection to ground, but it might connect to battery positive. To simulate that switch, you'll need to know which 'polarity' it is. There are ways to avoid figuring this out but in my opinion it's simpler overall to find this out.

To accomplish your "on" time, you could use a 555-timer IC circuit called a "one-shot" or monostable multivibrator. It can be set to whatever pulse length you want (up to a practical limit).
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
To accomplish your "on" time, you could use a 555-timer IC circuit called a "one-shot" or monostable multivibrator.
I thought of a one shot could turn it on. But what about turning it off after a few seconds?

My LED controller works off of negative inputs through its own onboard buttons.

Tony
 

wayneh

Joined Sep 9, 2010
16,162
I thought of a one shot could turn it on. But what about turning it off after a few seconds?

My LED controller works off of negative inputs through its own onboard buttons.

Tony
I admit I haven't thought it out completely. When the one-shot sequence ends, it will go from high to low, and you can use a capacitor to convert that to a brief pulse to ground instead of the continuous ground. I'm sure there's a way to get the negative going pulse at the start of the period also but I'm coming up blank at the moment. Somebody will likely remember. If nobody jumps in, I'll go find it.
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
Hi all

I have attached an operational drawing for the circuit I am asking for. I also made notes within the drawing of polarities and pulse timing. I hope the drawing makes what I am asking more clear.

The requested circuit must work on a typical automotive battery system. 9VDC to 13.8VDC ... When the prox sensor is trigger by motion. The prox sensor will emit a 700mS Ground pulse to the "requested circuit" input terminal. At approximately the same time this input pulse is received. An isolated Ground pulse (700mS minium) will be sent out the request circuit, to the "ON" trigger circuit of the LED controller. Also when an INPUT Ground pulse is received. A variable timer circuit will start in order to enable the output ground trigger pulse. An on-board resistor pot will be used to select the timing (3 to 15 seconds variable) to tell the "OFF" 700mS Ground pulse when to be emitted from the requested circuit. Until the 700mS GND output pulse has been sent out to the LED controller. Any other input trigger from the Prox sensor must be ignored.

I hope the above explanation, of the operation, for my requested circuit answers many questions.

I hope you guys can help me.

Thanks
TONY
 

Attachments

Last edited:

dl324

Joined Mar 30, 2015
9,582
An on-board resistor pot will be used to select the timing (3 to 15 seconds variable) to tell the "OFF" 700mS Ground pulse when to be emitted from the requested circuit. Until the 700mS GND output pulse has been sent out to the LED controller. Any other input trigger from the Prox sensor must be ignored.
That means the negative going pulse from the motion detector can trigger both the LEDs on and the one-shot circuit.
If it wasn't for the above complication. The way I understand it is that subsequent proximity sensor triggers are to be ignored until the 3-15 timer times out.
 

wayneh

Joined Sep 9, 2010
16,162
If it wasn't for the above complication. The way I understand it is that subsequent proximity sensor triggers are to be ignored until the 3-15 timer times out.
If the LEDs are already on, what does pressing the "ON" button again do? Nothing, if it's like my TV remote that has a separate ON and OFF buttons. Likewise the 555 will ignore a re-trigger during the one-shot period.
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
I just tried pressing the ON the button with the UNIT already ON. Every time the ON button is pressed. It initiates the startup flashing sequence every time the ON button is pressed. Not electrically damaging. But visually unappealing. Is there a way to lock out the ON pulse until the OFF button is sent?

TONY
 

dl324

Joined Mar 30, 2015
9,582
Is there a way to lock out the ON pulse until the OFF button is sent?
This is what I'm thinking.
upload_2018-6-18_9-9-20.png
On the first trigger event from the PIR sensor, two oneshots are triggered. The 0.7s closes the ON switch for the LEDs. The other is the variable delay for the off pulse.

When the variable oneshot is triggered, it's output will lock out any subsequent triggers from the PIR sensor. When the 3-15 minute oneshot times out, it will trigger another 0.7s oneshot that will close the off switch and re-enable triggering from the PIR sensor.

If you need more current than the inverter can source/sink, you'll need a logical equivalent. The variable timer will be difficult to control with a pot because the interval is too long for a 555 type timer.

If you use 555 timers, the triggers can't be direct coupled.
 

dl324

Joined Mar 30, 2015
9,582
Technically, a MC14538 could do a 15 minute interval. Pulse duration is R*C and the datasheet (Motorola) says maximum pulse duration is infinite; so it's limited by timing cap leakage and realistic maximum timing resistance.

2M ohms and 470uF would give about 900 seconds. There are two timers per package, they can be configured as non-retriggerable, positive or negative edge triggered, and they have complemented outputs, so the component count could come down.
 

wayneh

Joined Sep 9, 2010
16,162
I just tried pressing the ON the button with the UNIT already ON. Every time the ON button is pressed. It initiates the startup flashing sequence every time the ON button is pressed.
Ah, OK, so that is a problem that needs solving. I wonder if you could use the idea in @dl324 's circuit to inhibit any additional signal from the PIR itself during the one-shot period. Does the PIR have any control or "enable" pins or anything like that?
 

Thread Starter

stillgrowingup

Joined Jul 15, 2015
200
Top