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oss6000
08-08-2008, 06:41 AM
just a quick beginner question.....

when i connect a resisto between the Vdd and the Vss and check the voltage across that resistor using a multimeter, I get a pefect 4.98 ~ 5.00 volts

However, when I connect the resister between a BS2 pin and the Vss and measure the voltage (while sending a HIGH signal), I only get 3.17 volts.......... isnt supposed to be 5 volts as well??????

Mike Green
08-08-2008, 07:29 AM
It depends on the resistor value. The BS2 module's regulator (and the one on the HomeWork board) can supply in excess of 50mA before it reduces the voltage supplied (to protect itself). If you're using a Board of Education, that regulator can supply at least 1A. A Stamp pin can supply only about 20-25mA and not at full voltage. The MOS transistor between the Vdd supply and the I/O pin has a certain amount of resistance and that causes a voltage drop at high currents (like 20mA). The logic threshold for a Stamp input is about 1.2-1.4V, so a Stamp input pin will appear to be HIGH at any input voltage above the threshold, so 3.17V is still plenty high enough. The BS2 uses a PIC16F57 microprocessor. Download the datasheet from Microchip (the manufacturer) or from Parallax and look at the specifications for the I/O pin output voltage vs. current.

oss6000
08-08-2008, 09:48 AM
thnx alot Mike....that was very helpful

SRLM
08-08-2008, 11:10 AM
You could also use an oscilloscope to monitor the voltage and see if it drops right after you change a pin from low to high. This way you can get the time reference in.