Using a 555 timer how do we output a biphasic square wave instead of a monophasic? Is there any way to make it asymmetrical? If not are there any other devices or circuits to use to make an asymmetric biphasic output waveforms?
Electronic – Can you make a waveform asymmetrical with the 555 timer
555timerwaveform
Related Solutions
I think if you use a second 555, also connected as a monostable, but replace the timing capacitor with a short (and you don't need the timing resistor)-- triggered by the first one, that should work.
You could also use a D flip-flop such as a 4013 with the D tied high, but you'd need an inverter on the clock and a power-on reset circuit.
Or, something like this:
simulate this circuit – Schematic created using CircuitLab
C1/R3/D1 provides a semi-reliable power-on reset (100% reliable if the power turns on cleanly every time after a relatively long 'off' time where +V falls to near 0V).
C2 and R4 provide an edge trigger from the 555 output falling edge.
R1 and R2 protect the CMOS inputs
The problem with the reset circuit is that you have the reset hard tied to the 9V supply. The Transistor, when it turns in tries to short the 9V to GND.
Remove this connection and place a resistor from 9V to the RESET input. Something like 4.7K to 10K would be appropriate. Now the NPN transistor will be able to operate the reset input.
To make this a complete answer let me also add what others have already said about the MOSFET you are using to drive the nichrome wire. Connect the wire between the 9V supply and the drain of the MOSFET. Then connect the source of the MOSFET to GND. Now you will be able to switch a full 9V across the wire.
Best Answer
555 it is a legend bi or monostable oscillator with a quite sufficient accuracy (at around 1%~0,1%) and with stable operation. This general characteristics plus the low price mace this circuit to survive for decades. All this years of using, lot of “tricks” developed by the people they doing what they want it to.
But it is not a function generator and has it's limitations.
Maximum operating frequency is 300kHz - 500kHz
Duty cycle adjustment is not between 0% and 100% but it is within reasonable range (around 5% or higher and 95%). This can improve if you are use a 556: One to set frequency and the second as a one shot of variable width (duty cycle). But the same you can do with two opamp, at the same cost of 555!
The output of the 555 can be 0.5v to 1.5v above ground, so a trick is how to get a bipahse signal is to use a capacitor network and some load.
I can reccomend a good function generator that can build around an 8038 chip