I'm working on adding duty cycle control for a small project that used a 555 timer for a variable frequency square-wave generator.
For reasons of cost, development time and space, I would like to keep to a 555 timer based solution.
I need to be able to generate four frequencies: 0.1Hz, 0.5Hz, 5Hz, and 10Hz.
At each of these frequencies, I need to be able to vary the duty cycle: 50%, 30%, 10% and 1%.
After some research on the web, and reviewing a book on IC timers, this is the circuit I came up with:
The two transistors at the output of the TLC555 are to level-shift the output voltage swing from 0-15V to 0-5V
for the next stage. The supply voltage of 15V for the TLC555 was chosen to minimize the effect of having the two diodes
(and their voltage drops) in the timing circuit.
At this point, as the duty cycle is adjusted, the frequency changes also.
I would appreciate it if someone could advise me as to what modifications could be made to allow for separate, continuous adjustment
of the duty cycle and frequency, minimizing one affecting the other.
I realize there are digital methods to do this, but at this point, I need to look at the best I can do with the 555 timer.
Lastly, can anyone recommend a TLC555 based circuit using two TLC555s: a variable-frequency astable
followed by a variable on-time monostable?
Thanks much for your help!
Tom
