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How to lower voltage source from 5 to 1.5 volts? (Fez Panda II)


#1

I know there is a 5 volt voltage source on the Fez Panda II, but I need a voltage source of 1.5. How can I lower that voltage source from 5 to 1.5? I realize there may not be a way to do this progromatically, so I’m looking for some help understanding how it can be done with hardware components. Thoughts?

Thanks, Paul


#2

using a voltage divider: http://en.wikipedia.org/wiki/Voltage_divider


#3

Paul, there is only a 5v voltage source on the board, there is no 5v “output” port in the netmf sense of the word, ie you can’t set a digital pin to output 5v.

This is another case of knowing what you’re trying to achieve might lead to a more complete answer. A voltage divider is one way to do what you’re trying to achieve, but if for instance you need to use that for a very sensitive component, or wasted power is a concern, you may want to consider a voltage regulator.


#4

Thanks EriSan500 - Based off the following link:
http://www.raltron.com/cust/tools/voltage_divider.asp
it looks like I simply need to use 2 resistors. The question is what Ohm values should the resistors be? The above link provides a calculator, but it assumes the user is looking for the output voltage given some known Ohm resistors, instead of computing the Ohm values given a target input and output voltage.


#5

Brett, thanks for the clarification on terminology - I’ve updated the question.
Here’s the project: a potato gun!
I’m using an electric BBQ ignition component that runs off a single AA battery. Since the battery is 1.5 volts I figured I need to lower the voltage from the source on the Fez from 5 to 1.5. Is this the right approach?

Thanks, Paul


#6

How much current do you need to draw out of your 1,5v ? a single AA battery can provide more than 1 Amp, you’ll never get there with a voltage divider.

If you need some current (like an AA battery can provide) and don’t want to waste most on energy into heat, you might consider better a DC DC converter, such as this one for an example:


#7

Still the purpose needs to be known in more detail. Shall it replace the AA battery? Then there are voltage converters not needing too much steady current as a voltage divider.

If it needs to be a slow signal an analog output could be a solution.

for a faster pulse also schmitt trigger logic circuits operated at 1.5 V could help


#8

SteH, I added a diagram to the initial description - hopefully it will help clarify the intention.

You asked “shall it replace a AA battery” - yes, that would be ideal so I can just use one 9 volt battery which powers the Fez.

I’m not 100% sure, but I’m assuming it needs to be a steady current. The original unit is activated by simply closing a circuit to a single AA battery. While the circuit is closed there are sparks (about 4 per second).


#9

You definitly need a DC DC voltage converter.
However, don’t source it from your 5V from the FEZ, it will possibly overheat the oboard DC regulator, prefer to use it directly from your 9v battery, with possibly a little relay to trigger it from a digital pin on your FEZ, not to power the DC DC converter all the time when you don’t need it (and waste your battery power).


#10

Nicolas3, I like the idea of using a Relay, do you think something like this would work:
http://www.ghielectronics.com/catalog/product/192

I guess if I’m going to use a relay, I could simply use a AA battery. This would at least save me from buying the DC DC voltage converter. However it would require I use both a 9 volt for the Fez and a AA/1.5 volt for the igniter - tradeoff.


#11

Yes it will work, good idea !
However this kind of relay is a kind of a tank to kill a fly, you could use a way smaller one :wink: