Alternating potentiometers in Parallel to the base of an NPN Transistor

Hi Pix
No No No.
I don’t know exactly what you intend to do with this but certainly DO NOT connect the output (pin 3) to ground. I don’t know but it might destroy the 555. It certainly won’t do it any good.
Cheers Bob

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By the way, did you ever get that flip flop circuit to work.
I posted 4 days ago about my thoughts on that.
Please don’t join the brigade of people who don’t see fit to report results.
Cheers Bob

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Ohh good point.
Its going through a multimeter to ground… but it needs a diode there to protect the 555 timer!
Ill add it in soon

I did get it to work but as you predicted the led was a poor indicator. It would either be off or on. I.e. by the time i could get the led to illuminate at all the transistor was practically saturated and the potentiometer made next to no difference.

Hence why ive changed tack to a 555 timer circuit so i can measure the frequency instead and i can meausre if i was successful.

No its not. You have it connected directly to ground and for some unexplained reason the probe connected to that. If you want to measure anything connect a resistor from pin 3 to ground and connect your multimeter to pin 3
Cheers Bob
PS: At 500nF I don’t think C1 will be a polarised electrolytic capacitor.

Hi Pix
If you are just after an indication of what state the flip flop is in here is a quick circuit that is as simple as you will get.

The Op Amp is a common rail to rail. Non rail to rail Op Amps will not swing to 5V and ground.
I would suggest resistor value between 270Ω and 330Ω which will give a LED current of about 10mA which is within Op Amps capability.
Cheers Bob
The Op Amp and LED (3mm and 5mm) are available from Jaycar if that is more convenient.


To achieve a varying LED brightness you could use one of the LM3914/5/6 series. The IC turns on different outputs pins for varying voltage inputs. Connect different resistor values to the outputs and then to a single LED would change the current and thus the brightness.
You could also just implement a simple bargraph ( one pin sets dot/bar mode) and the observed brightness would increase as multiple LEDs are turned on.
For the datasheet look up the Texas Instruments WWW site.