A co-worker asked me to build a flashing LED circuit that is powered by solar panel (to charge batteries) and batteries only at night. He asked for minimal parts.
So far I build this prototype:

The only difference on protoboard is that instead of battery, I'm charging 2 x 4700 uF capacitors (I know, short time).
So far, it works, even on 300 uA.
Is there anything that any of the advanced users would add or change in this circuit?

 

What type of battery are you planning on, hope it isn't Lithium.

 

For now, i don't know, it's still a prototype on my protoboard.. Any suggestions? Battery should be fairly small in size.

 

Battery should be fairly small in size.

You can think of a battery as a voltage source + a very small serial resistor.

 

You could use the solar panel as the 'night' detector. With this circuit, the LED's will flash when the panel stops charging the battery.

 

With this circuit, the LED's will flash when the panel stops charging the battery.

What happens when the battery becomes fully charged during the day?

 

What happens when the battery becomes fully charged during the day?

There is no regulator to switch of the charging in that event so charging current will continue to flow and so the LED's will stay off.
This kind of charging is fine for e.g. NiCd and lead-acid batteries as long as the current is not too great.

 

You could use the solar panel as the 'night' detector. With this circuit, the LED's will flash when the panel stops charging the battery.
View attachment 107404

Thank You for the idea, will implement it in my project.

Battery will be NiCd, 4.8V (3200mAh)

 

A co-worker asked me to build a flashing LED circuit that is powered by solar panel (to charge batteries) and batteries only at night. He asked for minimal parts.
So far I build this prototype:
View attachment 107390
The only difference on protoboard is that instead of battery, I'm charging 2 x 4700 uF capacitors (I know, short time).
So far, it works, even on 300 uA.
Is there anything that any of the advanced users would add or change in this circuit?

One with fewer parts.
Self blinking LED, one transistor.
Resistor values may need to be adjusted.

 

Here is an alternate approach. Fewer parts, fewer soldered connections, a single timing element.

ak