555 timer only works when i disconnect pin 4 from V+ and touch the jumper

by wirl   Last Updated July 11, 2019 22:25 PM

I set up a pulse circuit on a breadboard with a 555 timer. Input voltage is 5 V. My values are roughly:

  • C = 100nf
  • R1 = 1K
  • R2. = 1M

I'm using the schematic shown at https://www.allaboutcircuits.com/tools/555-timer-astable-circuit/

This should produce 3 - 4 Hz at the output. When I power up the timer I get a frequency generated at about 150 Hz. Strangely when I disconnect the jumper from V+ (leaving it connected to pin 4), and touch the exposed end of the wire, the circuit works perfectly - outputting 3 - 4 Hz.

This is very weird to me. I tried some different resistor values and capacitors and it's the same result every time.

Any ideas?

Tags : 555


Related Questions