How can I regulate duty time and frequency of 555 timer output with 2 potentiometers?
Electronic – Control duty time and frequency with different potentiometers using one 555 timer
555
Related Solutions
If you need an accurate 50% duty cycle, a simple 555 circuit is not the way to go. A better method is to have an oscillator run at double frequency, where duty cycle is unimportant. Then feed that signal in a divide-by-two circuit and you'll have a perfect 50% duty cycle.
A simple divider can be made using a JK-flip flop where the J and K are high, like in this circuit:
simulate this circuit – Schematic created using CircuitLab
There are countless ways to create a 2-divider, all with their own advantages and disadvantages. A simple Google image search will give you pages full of them.
If I'm reading this question correctly you need two monostable circuits.
The circuits are both negative edge triggered monostables.
The first negative edge comes from the switch, S1, (this could be replaced by an NPN transistor if you want it to be triggered by another device). C1 and R2 produce a short spike from +V to 0V on the negative going edge of the input signal. This starts monostable 1 with R3 and C2 controlling the length of the pulse (T1) When the switch is opened diode D1 limits the positive going edge spike amplitude to 0.6V above +V, but this will not retrigger the monostable.
When the first monostable goes high R4 and C2 only allow the positive edge of this pulse through. D2 limits this to 0.6V above +V. This positive edge will not trigger the second monostable.
When the first monostable output goes LOW the negative edge of the pulse triggers the second monostable and its output goes HIGH for a period controlled by R5 and C4.
By having two separate monostable periods you can independently adjust the initial delay (T1) and the operating pulse time (T2)
Related Topic
- Electronic – Using 555 to generate square signal with fixed duty cycle / variable frequency
- Electronic – Producing different types of tones using the 555 timer
- Electronic – independent control of frequency and duty cycle in 555 timer (formulas)
- Electrical – Using Timer 555 to obtain a frequency multiplier
- Voltage Doubler – How to Use a 555 Timer for Voltage Doubling
- Timer – Appliance Countdown Timer Using Current Transformer and 555 Timers
- 555 Timer – Controlling a Servo with 2 Variable Positions Using a 555 Timer
Best Answer
Using two pots to adjust the frequency and duty cycle is easy, but there may be interaction between the controls. The simplest method is to have one pot for charge and another for discharge, with diodes steering the current between them. To change duty cycle you turn one pot up and the other down. To change frequency you adjust both in the same direction. That's a lot of interaction!
You can rearrange the pots so one controls duty cycle and the other changes frequency, but there will still be some interaction. Here's a circuit which has minimal interaction and provides a duty cycle range of about 2~98%. The practical frequency range is only about 3:1, and is quite sensitive at the low end.
simulate this circuit – Schematic created using CircuitLab
However there is a way to get wide frequency range with 0~100% duty cycle and no interaction, using the same number of parts! It uses the 555 as a triangle wave generator, and an opamp or comparator to control the duty cycle.
simulate this circuit