View Full Version : PropRPM

09-16-2007, 08:17 PM
I notice the propRPM only has one voltage regulator. Is it a 3V reg?

If you weren't going to use a keyboard, mouse, or anything that requires· 5V, can you power a Propeller·breadboard with only a 3V reg?

What are the values of the 2 electrolyic caps? (Are those electrolytic caps the input & output caps of the 3.3V reg?)


Post Edited (TonyA) : 9/16/2007 1:24:55 PM GMT

09-16-2007, 08:26 PM
The Propeller is designed to work at 3.3V. The only reason 5V is on some development boards is for compatability as some IC's require 5V to function.

09-16-2007, 08:38 PM
Thanks. You mean the IC's in the peripherals like the keyboard and mouse?

I just took a look at the schematic for the propRPM, so I see those caps (electrolytic) are the 3V reg input & output caps.

(Referring to the RPM schem describing the electrolytic caps of the 3V reg) I have never seen this before, what is "100 u / 16" ?

Does that literally mean divide 100 microfarads by 16? Or is it just a 100 uf cap?

09-16-2007, 08:38 PM
The value of the caps can be in a large range; the size of the "input" cap depends on the "ripple" of your power supply (which generally has to do with the current you draw from it). The "output" cap depends on specieal devices to add to the Prop. Servos are especially nasty.

Generally 100 uF will suffice for both.
It will even work without any, if you have connected the recommended 100 nF to each chip.

Edit: I just see your posting: "16" means "max 16 Volts".
Have a look into the host of basic electronic tutorials available!

Post Edited (deSilva) : 9/16/2007 1:43:18 PM GMT

09-16-2007, 08:45 PM
Ok, I see. the /16 is the max Voltage rating of the cap.

Would that power circuit (the one shown on the propRPM schematic) also work with a 9V battery?

Thanks again.

(Why would I need to read the boring tutorial when I have you?) <--joking

Post Edited (TonyA) : 9/16/2007 1:50:11 PM GMT

09-16-2007, 09:24 PM
But then you need not wait for anyones questionable replies...

You see, due to the construction of that kind of regulators, they draw the same current from the battery as is needed by the circuit. Say you need 250mA. The power not used is transformed ("dissipated") into heat within the regulator.

In that case it is 5.7V * 250 mA = nearly 1.5 W.

Which is much! It works but I should recommend an additional small heat sink.

09-16-2007, 09:48 PM
Excellent point.

Ok, I see.
Thanks again. I appreciate it.

Mark Bramwell
09-16-2007, 10:28 PM
I have the PropRPM. I like it. It only has 3.3v power on the board. I soldered in a 78L05 and used a fly wire to tap into the main power. I now have 3.3v and 5v available. I needed 5v because I am using an IR module (for TV remotes) and it would not work reliably at 3.3v

FYI: Since the IR module outputs a data signal at 5v, I used a 4.7k resistor between the IR_Out and the Propeller_IN pin. It is working rock-solid!

09-19-2007, 08:23 PM
Cool, thanks.