PDA

View Full Version : Problem: low I/O voltage



spccowboy08
01-31-2007, 01:49 AM
I am having trouble with the voltage output on my BS2. When a pin is set to high, the output voltage is only ~2V. The 9v battery powering the stamp is well charged and the Vdd output is still 5V. Any ideas what could cause this?

allanlane5
01-31-2007, 01:54 AM
What load are you trying to drive with that pin?

If that load wants too much current, this can happen.

Mike Green
01-31-2007, 01:57 AM
The Stamp I/O pins can only supply about 20ma of current. If you have too low a resistance load on an I/O pin, the high voltage will "sag". You should not see this kind of low "high" voltage normally. If you need to drive a higher current load, you will need a transistor buffer. Look at the "What's a Microcontroller?" tutorial that you can download via Parallax's website and the Stamps in Education page for information on how to do this.

spccowboy08
01-31-2007, 03:24 AM
Increasing the load resistance upped the output. Thanks.

metron9
02-02-2007, 01:57 AM
Measure the voltage across the load resistor, use ohms law to calculate the current draw.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!