bs2 pin always has some voltage even with 'low' command

shakil

Hi all,

we have to build a circuit where BS2 will have to provide control voltage[noparse][[/noparse]5v]
to a relay[noparse][[/noparse]through pin 14]·which will cause another circuit to deliver 12v to·a device.

we have tried the relay manually with 5v input and it works. but whenever we
connect it to the BS2·it·activates the circuit even when we have not issued a 'high 14' command.
also the relay does not cut the 12v power when we issue· 'low 14' command.

upon investigating we found that the BS2 pins allways has a very small amout
of voltage [noparse][[/noparse]<0.5v] present at its pins, even with a 'low' command.

we tried to use a pulldown registance to make the pin voltage 0 with a 'low' command but it did not work.

can someone suggest what should we do to make a BS2 pin to have· 0V?

thanks in advance.

** any example to control devices [noparse][[/noparse]using BS2 pins] with larger volatage requirements would also be very helpful·.

shakil

Jon Williams

How much current is required to activate the relay? Is it possible that you overstressed the I/O pin an damaged it?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

Mike Green

This may be normal. For input purposes, logic zero (low) is not zero volts and is defined as anything below 1.5 volts. Similarly, a logic one (high) is not five volts and is defined as anything above 3.5 volts. Outputs should produce 4.7 volts or greater for a high (for currents up to 18ma) and 0.6 volts or lower for a low (for currents up to 30ma). These numbers are taken from the SX48 datasheet which is available on Parallax's website, but are typical for most microprocessors (and other CMOS chips) these days.

Tom Walker

...and as I'm sure would have been noted before too long...

If you are trying to drive the relay directly from the Stamp pin, you may have already fried that pin. The Stamp's pins are not designed to source this much current and the back-EMF from releasing the relay will almost certainly smoke your Stamp pin. Several posts have been dedicated to driving high-current outputs and the "What's a Microcontroller?" text is a very worthwhile read...

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Truly Understand the Fundamentals and the Path will be so much easier...