View Full Version : Protoboard current: 35ma!?

02-20-2007, 05:30 AM
I'm observing something odd on my protoboard. When completely idle, running no code
(just a repeat waitcnt(0)) using the RC clock and nothing attached, it consumes 34.5ma.

This is true for all the protoboards I've tested.

The LED (which doesn't seem to be on the protoboard schematic, by the way) accounts
for 12.2ma by my calculations (I observed 2.93V across the "241" marked resistor which I
believe means it's a 240 ohm resistor).

By comparison, my demo board running the exact same trivial program consumes only
9.4ma (but my demo board doesn't have a power LED somehow).

Is this expected? Are the regulators consuming that much current idle? Or is there
something else that I'm missing?

This may have some implications for powering the protoboards off 9V batteries.

02-20-2007, 06:22 AM
Check the data sheet for the EEPROM - it's twice as large on the Protoboard.

02-20-2007, 06:48 AM
The EEPROM of the proto board is an Atmel At24C512, and according to the documentation should in idle mode only use a few (6) micro ampere. Even while reading it should not acount for much more than 2 mA.

Did you account for the low drop regulator? The LM1086 also uses a few mA in "quescient" mode, and there are two of them in series!

Maybe its also the pullup resistors of the I2C EEPROM interface, perhaps you need to set the I/O ports high, and to inputs after booting.


02-20-2007, 06:52 AM
looking at the regulator datasheet, you're loosing about 5~10ma per regulator, add that to the LED, eeprom and the hub, and it sounds about right at 35ma

Who says you have to have knowledge to use it?

I've killed a fly with my bare mind.

02-20-2007, 07:01 AM
For battery based apps, I'd recommended going for Switching mode power supplies, there's need some extra components, but savings on current consumption (for example from 9V battery) can be well over 50% compared to linear regulators usually used on eva-boards, as those linear regulators waste at least 2/3 of input juice.

Linear Circuits offers free SwithcerCad with plenty of example diagrams and simulations, link at their front page http://www.linear.com/index.jsp

This one looks good.. High efficiency (well over 90%), small, couple USD and little extra components needed for 5V or 3.3V output. LTC1877 - High Efficiency Monolithic Synchronous Step-Down Regulator http://www.linear.com/pc/productDetail.do?navId=P1881

Paul Baker
02-21-2007, 04:29 AM
Here is the preliminary current consumption graph for the Propeller under 4 different·tasks with all 8 cogs performing the same task at Ta=25C. In your situation the Propeller would consume under 5uA, everything else is due to other features of the board.

Paul Baker (mailto:pbaker@parallax.com)
Propeller Applications Engineer
[/url][url=http://www.parallax.com] (http://www.parallax.com)
Parallax, Inc. (http://www.parallax.com)

Post Edited (Paul Baker (Parallax)) : 2/20/2007 9:37:01 PM GMT

02-21-2007, 08:31 PM
This may be a little bit over the top, but I've built a couple of switching regulators for a project I'm doing. They accept input voltages of upto 50vdc and step it down to 5.1vdc. Max. power is 2.5 amps! www.farnell.com/datasheets/68012.pdf. (http://www.farnell.com/datasheets/68012.pdf.) Scroll down to page 10 and have a look at figure 26. I added a 3.3volt regulator to one of my power supplies to get power for the Prop.

I've built two for a project I'm currently doing. While it is designed to run on a 48vdc power supply, for testing I have been using a 12vdc power supply. Makes no difference to the output voltage. It would probably run on anything as low as 6 volts, though I haven't tested this. Anyway, heres a pic of my circuit boards : i157.photobucket.com/albums/t41/gyro_gearloose/Circuits.jpg (http://i157.photobucket.com/albums/t41/gyro_gearloose/Circuits.jpg)

Starting from the left we have both power supplies, then the Propellor board in the middle, and finally a dual stepper motor driver board. Of the two power supplies, the one at the top is a 5.1 volt supply for the motors, and the other is the 5.1/3.3 volt supply for the logic circuits (I need a 5 volt logic suppply as that is what the motor driver chips need)

If anyones interested, I can post the stripboard diagram I came up with (you can just see it in the background of the photo above). I used standard stripboard as I've never seen the point of adding the extra hassle of etching my own PCBs.

Post Edited (big_mark) : 2/21/2007 1:36:48 PM GMT

02-21-2007, 11:46 PM
Big_mark: Looks nice.. By voltage range, I'd say it soon reaches usability un automotive instllations :)

Stripboard is OK as long as it works, but I'd recommended cheap (1side) etch board for making more than one...
- better for high currents, less losses
- causes less RF interference (normally not problem on Hobbyboards).

03-09-2007, 12:44 AM
It seems like the same issue would be present using the linear regulators supplied with the propeller education kit. Have anyone tried using something like the MAX1674/1675/1676 parts in a breadboard? It looks like a good part to me for this sort of application. Just run the board off of a couple of AA batteries instead of a 9V.

03-09-2007, 07:44 PM
A suitable switching regulator would be the LT10732, or if the load is very light a linear regulator such as the Torex low drop low quiescent current regulators from the 6209 series would be suitable.