Modify circuit to power on/off Attiny85 by remote

Thread Starter


Joined Mar 18, 2024

Circuit B.JPG

I found this circuit online(Circuit A).
I modified it for my needs which is to start and shutdown an ATTINY85 using a tx/rx pair (Circuit B).
I'm running it on two AAA batteries.
The wireless receiver gives a long enough pulse for the Attiny to boot with no problem.
I wrote a rough code to drive pin2 high first thing on boot and reads for a high pulse on pin 5 thereafter to write pin2 low. it works well but I need to know if I've removed any important components or currently have any unnecessary ones (diodes for eg). I also have a few " for my information" questions about the original circuit.
3 queries:

1. If at some time in the future I had to replace my wireless receiver with one which was only able to supply a short pulse,
Is there a way to add a capacitor to the base of that transistor to sustain the pulse till gpio pin2 goes high.

2. Does there need to be a transistor between my wireless receiver output
and the 10k resistor or is it ok as I have it. My wireless receiver manual
is vague chinese but says "it's outputs are able to source less than 20ma at near VCC"
:)) specific) . When turned off it's wireless outputs are a flat 0v which allowed me to eliminate the 220k pulldown.
I'm not sure about the elimination of the 100k pulldown which seemed to be there to prevent a floating base. It works without it.

3. I saw the following comment below the original design:

"With this design, it need 16 mA to keep the circuit on. Not suitable for battery circuit. (5v -.7-.7)/220= 16mA + some low current via 100k

When the 2n3904 is on. The current is passing by the transistor instead of your 100k. Replace the 100k by 1M and replace the 220 ohm by a 100k. Will work fine :)
(5v from arduino-.7-.7)/100k= 36uA that's a lot better".

Would someone please explain what "passing by the transistor" means and is that analysis correct.



Joined Jun 8, 2013
Wireles receiver is quite typical 4 programmable outputs that can that can lock high on remote press or pulse. Voltage range is 2.2 to 5V. Define "strange" on Circuit B.
Maybe so, but not how you've drawn it.
Is there independent input and output connections for the xcvr in circuit B?

Thread Starter


Joined Mar 18, 2024
Maybe so, but not how you've drawn it.
Is there independent input and output connections for the xcvr in circuit B?
I'm honestly not sure what you're asking. All the wireless receiver does in circuit B is replace the switch in circuit A with almost no difference in impact or outcome. I'd love to answer your question because I come here to learn If you could make clear in plain language which part of the circuit you find to be troublesome.


Joined Jul 29, 2018
Regarding the 100K base pulldown: yes it "works" without one but it might not be reliable. On a different transistor or when hot the collector base junction might become leaky, causing the unit to stay on continuously. Putting the resistor in place keeps the base close to ground under all expected "off" conditions.