Hello,

I made a ciclo-computer that measures the speed and distance you travel by bicycle (attiny microcontroller and 7 segments LED display). Currently it is running on one 9V battery which lasts for about 8 hours.

My plan is to use a dynamo to charge the battery. To do this I have to cut off the power to the pic while the battery is charging ? If yes I would like to use 2 batteries and switch between them while one is charging. How could I switch between batteries and not make the microcontroller to reset? Do I use a capacitor?

Thanks,
Bogdan

 

How about use the battery as backup.

What is ur dynamo power rating ?

 

Are your 9V batteries the rechargeable kind?
Are they Ni-Cad or Ni-MH?
Are they actually 7.2V or 8.4V?
Do you have a charger circuit?

 

The dynamo is a 12v 6W. My batteries are NIMH rechargeable 8.4 volts.
The charging circuit is not the hard part ... I don't know if I can charge a battery and power my circuit in the same time. If this is not possible then how do you switch between the batteries without power interruption.

 

with 6W you can charge and power a typical circuit like urs.
But need to see ur circuit to say anything abt it's power drain.

 

I think that the dynamo will deliver 6W only at high speeds. During the time I stop at a semaphore or go slow I need to power my circuit with a battery.
So I need to solve the problems from my first post.

 

Can you switch from LED to LCD display?
Your battery will last a lot longer.

 

I thought about using a LCD but I want to do this battery recharging stuff to learn something about battery management.
How dose a mobile phone keep functioning while it is charged?

 

why not try and reduce the power usage of the current system e.g.: turning things off when not needed even for a couple of mS? then implement a charging circuit?

 

I want to build the charging circuit anyway regardless of how much power my system needs. I would like to use a battery and when I have the right speed to produce enough energy from the dynamo to power the circuit and charge the battery I would like to cut off the power from the battery and power my circuit from the dynamo.

How do I make this switch between the battery and the dynamo without interrupting the power to the microcontroller?

 

Use a diode.