I was wondering if there is a way to drop 5v down to 3.3v without using a voltage regulator.
Maybe just using a diode and a resistor or two.
I use a botboard 2 and an atom pro 28.
I read somewhere that IO 6 and 7 on the botboard have a 3.3v output so setting pin7 to high would work as i only need very little power 20mA max. Giving the pin6/7 are infact 3.3v
It’s for a low power bluetooth to uart serial adapter which is designed to only use 10mA during continuous data transfer.
I’d prefer to minimize the components and cost, the radioshack here only has 5v and 12v regulators.
Edit: I’ve confirmed pin7 outputs 3.0v when set to high.
Which is odd, and i noticed pin 11 outputs 4v instead of 5, no biggy still works.
Now i need to know, will pin7 be able to output the 10mA i need? (20mA to be safe)
My electronics skills are real real rusty, but if I remember correctly you can use two resistors to do this. For example if you have a 10K and a 20K resistor, where you connect it like:
+5v -R1(10K)-+-R2(20K)---GND
|
~3.3v
The voltage drop across the first resister would be (r1/(r1+r2))*v. How much current that will go through this also depends on the values of r1 and R2. For example if r1 and r2 were 1ohm and 2ohm, you would get the same voltage, but be eating a lot more current…
Hopefully one of the less electrically challanged people can correct this
That will work as a voltage reference, but as soon as you draw current into a load through it, the voltage will change. There are other problems with this solution, as described here:
I’m not sure what the definition of “pricey” is, 3.3V regulators are “inexpensive”. I suspect the application you want to use this for requires a stable supply. You could try the following technique (note that it requires a zener diode).
Radio shack has the below adjustable regulator, but it will require additional parts. Another possibility might be using a low resistance pot (bottom) as an adjustable voltage divider. Put it in the circuit with the output voltage set low and connected to the load. Then carefully increase the output voltage to the load until it is ~3.3v. Inexpensive 3.3v voltage regulators are available from online suppliers, but there is always the ~$8 s/h in addition to the part cost.
