74HC74D initial output value after power up

Question

I use a touch sensor (Active Low) to light up a light bulb. here I've used a 74HC74D D flip flop to turn on an off the bulb with the sensor pulse (sensor output is active low which is then converted to a active high with a PNP transistor to make the flip flop work)

my problem is that at the power up the state of the output is not determined. Is there a way to make the output zero at the startup to ensure an powered off bulb at the start up the circuit?

Answer 1

One solution is to use the CLR pin of the flipflop. Place a capacitor to GND and a resistor pulled up to Vcc on the pin. This will create a delayed low level on that pin at power up to clear the flop.

The RC time constant needed will depend a lot on the rise time of the Vcc at power up.