unused pins starting issue

waltsailing

Hi,

I have build a circuit·which uses·a programmed·BS2PX24 and it is on its own board.··Sometimes the thing does not start up right.· I have three boards built up and they are programmed differently and they all seem to exibit this issue randomly.· Switch the power off and on and it often comes on on the second or third start try.· Then runs fine (Except if using sleep commands) but that is a seperate issue.··The board is etched (express PCB)·and soldered, so I do not suspect the construction (Socketed·stamp).· ·The program is pretty·simple and I do not suspect it. ·Does anyone know what·is the·recommended way on the board to terminate unused pins like the programming pins, reset, and bypassing?·· I have no programming interface directly on the board,·i.e., cap's or transistors for connection to programming or debug.

I am suspecting

Thank You,
Walt,

MrBi11

just wondering, is your power supply on these boards well regulated/filtered?

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waltsailing

Hi, Thank you for the quick response. Here is the configuration.

4 AA batteries, with LDO linear M2940CT. input of Low drop out regulator is 220 uF, output has two 1000 uF caps. These are within 1/4 inch of LDO and Vcc traces to the stamp are less than 1 inch, approx .050 inch wide. The ground is full plane, filled top and bottom of board where there are no traces. I will be putting in a a .01 or .001 on the power lines for the stamp Vdd pin to ground and also the Vin pin 24. Raw battery power (6 Volts) is applied to the vin pin and regulated power from the LDO is applied to the Vdd pin 21. Reset pin is not connected on stamp, nore are the three programming pins, 1,2, 3.

I connected my external LDO to the Vdd pin on 5 volts. Now looking at this, not sure if it is necessary or not or a good idea. Maybe it should be isolated. Thinking about it I might be able to scrap the LDO regulator and run off the stamps regulator. The stamp may have sufficient power for the circuits on one of my boards, but not all of them as the LDO regulator has a 10 ma idle current.

Walt,

MrBi11

It's not a good Idea to use both an external regulator [noparse][[/noparse]to Vdd] and the on board regulator [noparse][[/noparse]Vin] at the same time.

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Tracy Allen

A set of 4 AA cells does not have quite enough voltage overhead to power BASIC Stamp projects for long, and that would be especially true of the more power hungry BS2px. The voltage regulator LM2940 requires 5.5 volts on its input in order to supply 5 volts to the Stamp. Look at the attached voltage curve for the Energizer AA Alkaline battery and note how rapidly it falls off from the nominal 1.5 volts per cell. The regulator needs at least 1.375 Volts per cell at the input in order to add up to the needed 5.5 volts. The BS2px draws over 50 milliamps at 5 volts, which is 250 milliwatts right there, plus the regulator quiescent current and other loads.

Try powering your project from a more robust source, and see if that helps with the reset problem.

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Tracy Allen
www.emesystems.com