Hello good folks,
I built this four decades digital counter but there are strange happenings! When I run the counter off my 7805 regulated 9V battery (plus 2x 1uF electrolytic caps), it sits there waiting for the input signal with all counters displaying zero as it should. When I run it off my 7805 regulated power supply, it just starts counting while receiving NO input signal when my hand is held close to the PCB and WITHOUT touching anything. When I take my hand away, the counting stops.
I have added a 470uF electrolytic cap between the + and - of the digital counter but it still counts by itself when my hand is close to the PCB.
The power supply was built from a kit and either side of the 7805 there are 22pF caps (nonpolarised). Would it help if I change these two caps to 1uF electrolytic caps. Why is my counter "ghost" counting? Does it possibly have anything to do with impedence? ( Don't really know what it means but sounds good!)
When connected to my Digital pulse generator, no problems at all. It waits for signal input without counting, even though it is connected to the power supply. When running the counter off regulated 9V battery, no "ghost counting" at all, with or without signal input.
Thank you.
Barry.
Here is a circuit of one digit of the four digit counter:[/img]
I built this four decades digital counter but there are strange happenings! When I run the counter off my 7805 regulated 9V battery (plus 2x 1uF electrolytic caps), it sits there waiting for the input signal with all counters displaying zero as it should. When I run it off my 7805 regulated power supply, it just starts counting while receiving NO input signal when my hand is held close to the PCB and WITHOUT touching anything. When I take my hand away, the counting stops.
I have added a 470uF electrolytic cap between the + and - of the digital counter but it still counts by itself when my hand is close to the PCB.
The power supply was built from a kit and either side of the 7805 there are 22pF caps (nonpolarised). Would it help if I change these two caps to 1uF electrolytic caps. Why is my counter "ghost" counting? Does it possibly have anything to do with impedence? ( Don't really know what it means but sounds good!)
When connected to my Digital pulse generator, no problems at all. It waits for signal input without counting, even though it is connected to the power supply. When running the counter off regulated 9V battery, no "ghost counting" at all, with or without signal input.
Thank you.
Barry.
Here is a circuit of one digit of the four digit counter:[/img]