How to cancel out only first High signal while receiving to remaining ones

Question

I have an motion sensor that sends the high signal each time it is connected or turned on (beside the times when it actually detects motion).

The sensor is set to trigger an alarm each time it sends the high signal, so when it starts, it also triggers the alarm although no motion was detected.

Is there a way to cancel out that first signal so that only remaining signals with actual sensor data (after the first one) would be captured in the circuit?

The sensor and the alarm run on 6V DC. If possible, I would want to implement this with basic electronic components such as transistors, capacitors, resistors, etc, without having to buy some expensive IC.

Update: I have added the scheme

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

I would want to implement this with basic electronic components such as transistors, capacitors, resistors, etc, without having to buy some expensive IC.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. R3 and C1 provide a 1 s turn-on delay. Scale to suit.

A CD4011 will provide four NAND gates for about €0.35.

---

Figure 2. The RADAR module schematic with enable input highlighted.

The module has an input marked ENABLE which seems to be called CDS in the text. The authors say it has a light dependent resistor to disable the unit at night but don't seem to be sure why. If the LDR is not present then you could try adding a capacitor between ENABLE and GND to create a power-up delay. Given that R15 is 1M a value of 1 to 10 uF seems appropriate.

Answer 2

You can build logical AND gate with transistors:

Where the A signal would be connected to your motion sensor, and B signal would be connected to RC charged capacitor. Imagine capacitor that is initially discharged. After turning the device on, through a big resistor it starts charging, until it reaches some voltage required the transistor to turn on. Try with values R=100k, C=100uF, or calculate the time constant precisely. Dont forget to put some huge resistor in parallel with C, so after turning the device off, it will fully discharge the capacitor.

Simulate the scheme in falstad. I had to move the resistor from emittor to the collector, so it produces negated output (NAND), with third transistor we invert it back to get AND gate. The simulation in falstad is quite slow, so I set the pulse generator to 20 Hz and also reduced the capacity 10x. From the simulation you can see that when the capacitor reaches about 0.7V, it opens the transistor on bottom, the second transistor is triggered by signal generator (motion sensor)