I am starting to work with Wireless RF. The transmitter can operate between 2 - 12 Volts (a 9 Volt battery works just fine which is good because it is small in size).
So basically I need a way to power the reciever now, which operates between 4.5 to 5.5 Volts and 3.5 to 4.5 mA. Since the Transmitter uses a small and convenient 9 Volt, I thought using another 9 Volt for the reciever would be better than using a more bulky three AA’s. Plus I can’t even find a battery holder that takes three AA’s.
So I created a voltage divider with another 9 volt battery by connecting a 1K resistor to the positive lead, then connecting a 33K resistor to the end of the 1K resistor to act as the bleeder. Then I connected the Reciever to the end of the 1K as well. I can’t remember what the exact measurements of voltage and current were while hooked up to the reviever but I think the voltage was 4.94V and current was 4.34mA.
I then continued to test the Transmitter and Reciever out. I sent a signal from the Transmitter to the Reviever which had an LED that would turn on. The LED would turn on(sortof), but it would blink very quickly instead of a solid glow. I decided to take the LED out and measure the current and voltage the LED was getting. I then found out that the voltage was fine, but the current was fluctuating. It would slowly climb up to 2.90mA and then slowly fall back to 2.60mA and the process would continue. This is obviously why the LED is blinking and not staying fully lit.
Can anyone tell me what I am doing wrong here?
Or does anyone know a different solution to this power supply situation?
by your calculations the voltage divider should give 4ma. The receiver takes 4 ma, so whats feeding the LED? led at normal brightness need quite giid amount of current
I’ve powered the reciever once before by using a lower voltage and lower current than what I have used here. So I’m fairly confident that the problem has to do with the fluctuating current, which I have no idea why its fluctuating.
Powering anything with a resistive voltage divider is a HORRIBLE idea. If the current the device uses changes AT ALL (as it would when the LED tries to come on) the input voltage will drop in proportion to the current change. Also, if the device ever goes to sleep or something similar and REDUCES its current draw at all, you could give the device a nasty surge in voltage again relative to the current change.
You need to use a regulator… I guarantee it will fix all your problems.
nothing better cheaper and more user friendly than the 78L05. any way can you tell us what transmitter and reciever you are using and what is the circuit configuration, otherwise we are all just guessing. i would be very interested to know what sort of output the led is connected to.
I can now see why using a voltage divider is a horrible idea. Thank you mpanetta for pointing this out! But I was just told by someone that using a 9 Volt battery in general would not be suitable for this application because I would have to replace them frequently. So I guess a voltage regulator wouldn’t save me here either.
Now I am completely lost on how to power this thing! It looks like using 3 AAs is the only solution Too bad I can’t even find a simple battery holder for 3 of them. And oh, I guess the transmitter needs 5 volts as well instead of the 9 volts I thought I would need. I didn’t test out the 9 volts on it yet thankfully.
If anyone is kind-hearted enough to try to help me out with this here is a link to the whole schematics and what not.
Travis456:
Now I am completely lost on how to power this thing! It looks like using 3 AAs is the only solution Too bad I can’t even find a simple battery holder for 3 of them.
They also have 4xAA holders that will provide 6V if your transmitter can take that.
If you’re going to get into electronics as a hobby, one of the most important things is to learn who all the various parts vendors are and what they specialize in.
If you are using a 9V you will get about 80 hours of work so if it was receiving constantly all the time. With 1 AA battery it will be the same. You best bet will be 4 2000mAh batteries with a LDO regulator if you can afford the space or a lithium if you can afford the cost.
This might be perfect. I was not aware they had these!
You seem to know a lot about the various electronic parts/peices they have out there. Do you have an idea how long this power supply would last for my receiver application?
angelsix
If you are using a 9V you will get about 80 hours of work so if it was receiving constantly all the time. With 1 AA battery it will be the same.
If this is true when using the 5V DC to DC Step Up - 1xAA, then my problem is solved.
If it does not last very long, what about running two of these things in parallel?
Two batteries in parallel will certainly have an impact on battery life.
I wouldn’t bother with two step-up converters in parallel unless one is deemed to have insufficient current-supply capability, and even then, a higher-rating power supply is a better option IMHO. You might see an increase of battery life this way, but probably not as much as just running the one converter with a bigger battery/more batteries (in parallel).
Too bad I can’t even find a simple battery holder for 3 of them. And oh, I guess the transmitter needs 5 volts as well instead of the 9 volts I thought I would need. I didn’t test out the 9 volts on it yet thankfully.