Go Down

Topic: Solar powered ATtiny85 "hanging" during startup (Read 5244 times) previous topic - next topic

Coding Badly

I haven't determined what the voltage is when the BOD puts the AT85 into reset.

So you have the BOD enabled?  At what voltage?


You are above my pay grade.  I have no idea how to enable/disable the BOD.   I just write some arduino code and use the IDE and my MEGA 2560 to download a sketch to the ATtiny85.  I've done several examples this way and so far they all work fine.   I'm fine with the BOD stopping the AT85 from running when the voltage drops.  That is going to happen every night until the solar cell finally doesn't send any voltage or current to the AT and it just stops.  I don't mind that the AT is not running at night.  It's the next day start up that is a problem. Because the solar cell brings up voltage and current slowly as it gets more and more sunlight it eventually sends enough voltage to the 7805 to power the AT85 because my power on led is on, but I always have to disconnect and reconnect power from the solar cell to get the AT85 up and running.  Again, I'm pretty sure it's because once the AT85 has enough current to run and it does start, it immediately stops because the AT starts using leds and sensors that cause the current to drop too low.
I was thinking that maybe a TIP120 could be used to insure that there is enough current to run the AT85 AND the leds and sensors before it powers on the AT85?  If not a TIP then maybe something else that would work like the 7805 does with voltage, ie; minimum of 7 volts before it starts outputting 5 volts, but with a minimum amount of current at say 100mA.


I didn't know the 7805 would not disconnect when voltages dropped below 7 volts.  But it doesn't really matter as long as it doesn't start passing 5 volts until it gets at least 7.  Funny thought about a bird flying over.  I tried using my hand to simulate a bird and nothing happens.  I think the solar cell is providing almost 500mA at peak so clouds, birds, hand passing overhead, etc. don't lower the output enough for the circuit to stop.

There are few ways allow you to do it. I list 2.

1. LTC4365 - Linear Technology
UV, OV and Reverse $3.69
Supply Protection Controller IC (turn off power)

2. ON Semiconductor
MC34064 $0.33
Undervoltage Sensing Circuit (reset Arduino)

I list them here as bandages not solutions, but if I were you, I will go pito -Reply #4 direction.

Coding Badly

I have no idea how to enable/disable the BOD.

No problem.  Which core are you using?


You will be far better off using a small battery.
The battery is not for running the Micro over the night, but is there to ensure that in low light in the morning when the Solar Panels voltage rises
sufficiently high to start the ATtiny, there is enough current available to run it.
Solar cells dont have a linear voltage / current relationship.
The voltage with no load rises at a logarithmic rate whilst the current capacity rises at a linear rate for a given illumination.
What happens with no battery, is that the solar voltage will rise quickly to above 5 V , which will cause the 7805 to start operating, but the solar cell has no capacity to deliver any current , so the voltage immediately collapses, and the Micro stops.


Exact analysis Mauried.  That is what is happening and that is what I was trying to describe.  It makes perfect sense to include a battery after what everyone has told me.  This is the second time I have used the forum to get help and I am just amazed at the amount of help out there and the incredible knowledge base  that it comes from.  Many thanks again to everyone that participates.

Go Up