Hello,
What could be the reason that makes the voltage of a 9V battery drop every second? Im trying to build a line-follower robot, and I'm doing the circuit in a general purpose PCB (the one with holes). I'm using a MCU (PIC16F877A) and in the beginning I had only the DC motors connected and it was all good, but after I connected the CNY70 the problems started. The circuit I'm using is:
The only difference between the circuit and the design is that I've connected the CNY70 to 3V instead of 5V, and I've only connected two of them so far. In the PCB, once I turn the switch on, suddenly the voltage of the 9V starts to drop to the point where it can't power my MCU anymore.
Thanks.
One way or another, too much
One way or another, too much current is being drawn from the 9V battery. There are 3 realistic possibilities to explain this:
• Short circuit. Either due to a connection mistake, solder bridge, or similar problem there is a connection between the supply and ground where there shouldn’t be.
• Low motor resistance. Not all that likely, but if you’re using big motors they could potentially be drawing more current from the battery than it can handle.
• 9V is running low. 9V batteries are notorious for not being able to provide high current output, and this only gets worse as they are depleted. Even if the battery reads close to 9V when you test it, it may be somewhat worn out, and therefore it will have even lower current capability.
Thanks for the reply! I was
Thanks for the reply! I was really clueless why would that happen, I though that if I had a short circuit somewhere, everything would just stop working, but I didn’t know that it could be the cause. Anyway, before I posted in here I “resoldered” (not sure what the right term is) everything in the PCB, checking after every solder for short circuits, so there is a smaller chance for this to be the cause.
But, when you said that it could be because the 9V is running low, I think you are right. I bought it some weeks ago and now when I measure its voltage with the multitester it says ~6V. I didn’t know this kind of things happen when the battery is running low. I’ve heard before that the 9V batteries doesn’t last long, so thats why though of connecting only the MCU to it, but I did connected the motors a few times to it, so that might have pulled a lot of current.
Again, thanks for the message, I will go and try with another 9V battery to make sure that was the problem.
You might already know this,
You might already know this, but a 9V is (usually) made from 6 tiny AAAA cells soldered together and wrapped into the familiar little rectangular 9V blocks. If your 9V battery shows a terminal voltage of only ~6V, then each of those little AAAA’s is producing ~1V, which is what you’d expect from an alkaline cell at the end of its energy capacity.
If using a fresh 9V makes everything work as expected, then it might be worth considering switching to 6 AA cells in series to replace your 9V, or some other option with a bit more stamina (plus 9V batteries are often quite expensive for how much power they deliver…).
Good luck =D
Nice idea, I haven’t
Nice idea, I haven’t connected the six sensors yet, just two, but I might do what you suggested when I connect the other four, thanks for the great tip!
