# Alternating potentiometers in Parallel to the base of an NPN Transistor **URL:** \ **Category:** Uncategorized\ **Created:** [27 March 2024 03:26 UTC](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516 "2024-03-27T03:26:32Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![Robert93820](https://avatars.discourse-cdn.com/v4/letter/r/ac91a4/32.png) [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)\ **Post date:** [1 April 2024 00:45 UTC](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516/21 "2024-04-01T00:45:21Z")
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 ---
**Author:** ![Robert93820](https://avatars.discourse-cdn.com/v4/letter/r/ac91a4/32.png) [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)\ **Post date:** [1 April 2024 00:48 UTC](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516/22 "2024-04-01T00:48:03Z")
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 ---
**Author:** ![Pixmusix](https://yyz2.discourse-cdn.com/flex028/user_avatar/forum.core-electronics.com.au/pixmusix/32/9719_2.png) [@Pixmusix](https://forum.core-electronics.com.au/u/Pixmusix)\ **Post date:** [1 April 2024 00:49 UTC](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516/23 "2024-04-01T00:49:19Z")
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 ---
**Author:** ![Pixmusix](https://yyz2.discourse-cdn.com/flex028/user_avatar/forum.core-electronics.com.au/pixmusix/32/9719_2.png) [@Pixmusix](https://forum.core-electronics.com.au/u/Pixmusix)\ **Post date:** [1 April 2024 00:54 UTC](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516/24 "2024-04-01T00:54:12Z")
> [@Robert93820](#): > > By the way, did you ever get that flip flop circuit to work. 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. ---
**Author:** ![Robert93820](https://avatars.discourse-cdn.com/v4/letter/r/ac91a4/32.png) [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)\ **Post date:** [1 April 2024 01:34 UTC](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516/25 "2024-04-01T01:34:48Z")
> [@Pixmusix](#): > > Its going through a multimeter to ground 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. ---
**Author:** ![Robert93820](https://avatars.discourse-cdn.com/v4/letter/r/ac91a4/32.png) [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)\ **Post date:** [1 April 2024 02:03 UTC](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516/26 "2024-04-01T02:03:53Z")
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. ![image](https://canada1.discourse-cdn.com/flex028/uploads/core_electronics/original/2X/d/dcc3f017804b925ed73b20c2912a13ea0433c620.jpeg) 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. ---
**Author:** ![dave50358](https://avatars.discourse-cdn.com/v4/letter/d/e480ec/32.png) [@dave50358](https://forum.core-electronics.com.au/u/dave50358)\ **Post date:** [1 April 2024 21:01 UTC](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516/27 "2024-04-01T21:01:57Z")
Pix, 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. Dave [Previous page](https://forum.core-electronics.com.au/t/alternating-potentiometers-in-parallel-to-the-base-of-an-npn-transistor/19516.md?page=1)