Create new (adjusted) pulse from old

Thread Starter

Henk Wijtman

Joined Jun 17, 2021
9
Hi,
I have an input pulse trigger signal (from LED) that first triggers 5 times (high/low 4.5/2.5v - 1sec interval-) and after that it stays low for 30 sec’s and than goes high again. I need to create a pulse trigger signal out of this trigger that only fires high when the input pulse stays low longer than 1 sec.
So It has to skip the short (1 sec interval) pulses. The final output trigger stays high as long as the long input (long ± 30sec) pulse stays low.

Circuit1.png

Is it possible to make such an electronic circuit ?

It seems it can be done by an RC filter with a zener diode as threshold
When the capacitor is charged by the 1 sec pulses it does not reach the zener threshold
The 30 sec pulse charges the capacitor fully so the zener diode starts conducting. With a
logic buffer in the end the signal can be shaped 0 and 1.

The input pulses have a negative value so I do not know how to design the circuit and I also
have no knowledge of the resistor, capacitor and zener values.

please help

Henk Wijtman
Rotterdam
Netherlands
 

Thread Starter

Henk Wijtman

Joined Jun 17, 2021
9
DickCappels,
Thank you for answering. I have drawn a very clumsy idea because I have very little knowledge of electronics. It's assembled from circuits on the internet and partly my minimal electronic logic.

Circuit2.png

And AnalogKid a will look up the 'missing pulse detector' ?
Please comment
 

MrChips

Joined Oct 2, 2009
24,609
I offer this circuit. There is no guarantee that it will work for you. You need to play with the component values.

I need to know the resistance of the relay and current and voltage required to operate the relay.

I also need to know how much current is supplied by the input signal.
Is the timing 0.5-second on and 0.5-second off?

AAC relay.jpg
 

Thread Starter

Henk Wijtman

Joined Jun 17, 2021
9
MrChips
I will try the circuit and keep you posted. Could you explain the circuit to me so I am learning something too.
This is the relais I am using.
Relais.png
 

eetech00

Joined Jun 8, 2013
2,644
Hi,
I have an input pulse trigger signal (from LED) that first triggers 5 times (high/low 4.5/2.5v - 1sec interval-) and after that it stays low for 30 sec’s and than goes high again. I need to create a pulse trigger signal out of this trigger that only fires high when the input pulse stays low longer than 1 sec.
So It has to skip the short (1 sec interval) pulses. The final output trigger stays high as long as the long input (long ± 30sec) pulse stays low.

View attachment 241464

Is it possible to make such an electronic circuit ?

It seems it can be done by an RC filter with a zener diode as threshold
When the capacitor is charged by the 1 sec pulses it does not reach the zener threshold
The 30 sec pulse charges the capacitor fully so the zener diode starts conducting. With a
logic buffer in the end the signal can be shaped 0 and 1.

The input pulses have a negative value so I do not know how to design the circuit and I also
have no knowledge of the resistor, capacitor and zener values.

please help

Henk Wijtman
Rotterdam
Netherlands
Here is an alternative circuit.
This is a Missing Pulse Detector as mentioned in post #3.
The input signal responds to logic level of 4.5v=high, 2.5v=low. If no input pulses are detected, the relay remains energized. If pulses are detected, relay becomes de-energized.

1623958685283.png
 

MrChips

Joined Oct 2, 2009
24,609
The relay has a DC coil resistance of 167Ω and operates at 30mA @ 5V.

I used a 2N3906 PNP bipolar transistor because it matches your 5V/2.55V input nicely.
With 5V supply, the transistor needs greater than 4.5V to turn off and lower than 4.3V to turn on.
To drive the relay with 30mA we want to turn on the base with about 3mA.
With the values of R1 = 1k and R2 = 750, the base current is about 1mA which should be ok.
The value of C1 = 4700μF is higher than I would like but 1-second intervals don't give us much choice.

I have shown simulations with two different time intervals.
The first simulation is with 1-second inputs ON and OFF (A - green trace).
C1 holds the voltage above 4.3V (B - yellow trace) and keeps transistor Q1 in the off state.
C - cyan trace is the voltage on the relay.
AAC relay3.jpg


In the second simulation, the signal is on for 10 seconds and off for 10 seconds (A - green trace).
The voltage on the base falls below 4.2V (B - yellow trace).
The voltage on the load R3 is switched on at 4.8V (C - cyan trace).
AAC relay4.jpg
 

Thread Starter

Henk Wijtman

Joined Jun 17, 2021
9
Hi you all,
I want to thank you for all answers I've got for 'my' electronic problem. I am a very electronic newbe (even have to lookup the pinout of a transistor) but through your answers I am learning a lot. I am going to experiment now and let you know the result (or more questions ?).
Thanks again
Henk
 

Thread Starter

Henk Wijtman

Joined Jun 17, 2021
9
YES!! Just put the circuit of MrChips in test together and it works like a charm. Gonna build it into the alarm now. I bought the smallest 4700uf (16 v) I could get and hope it wil fit inside the enclosure.
Thanks again
 

MrChips

Joined Oct 2, 2009
24,609
just a thought: would a resistor in series with the base be useful for when power is first applied?
Good point.

There is a large current flowing through the emitter-base junction in order to charge the capacitor from 0V to 5V on first power on. Placing a 100Ω resistor in front of the base would reduce the current.

An alternative is to move the capacitor C1 and place it across R2, keeping the positive terminal at +5V.
AAC relay5.jpg
 

Thread Starter

Henk Wijtman

Joined Jun 17, 2021
9
Hi,
I just implemented the latest modification to the circuit (moved the capacitor across R2). But now the the relais already reacts on the last 2 of 5 pulses. I think I have to make an adjustment to one of the resistors. But which one and how much.
 
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