problem with "Polling the RC-Time Circuit with the BASIC Stamp" Ch.5

Matthew

Is there something wrong if my timer goes above 4 minutes in the "Polling the RC-Time Circuit with the BASIC Stamp" Ch.5 activity from "What's a Microcontroller?"? The Stamp charges the capacitor for only 5 seconds, so if it takes longer than 4 minutes I'm assuming something is wrong. I just took off the power once it went past 4 minutes because I was worried it might explode or something (there were TONS of warnings in this chapter about the capacitor exploding).

Andy Lindsay (Parallax)

The valid time range is between a couple seconds for the 470 and a couple minutes for the 10 k. Four minutes is definitely too long.

If the resistor in parallel with the capacitor (R1, R2, etc) has wimpy leads, it may not be making contact with the Vss terminal. This would cause the 3300 uF capacitor to hold its charge for a very long time. You could try inserting a jumper wire into the Vss socket (same one as the wimpy resistor lead) to ensure electrical contact. Leave the other end of the jumper wire disconnected, and make sure it doesn't touch anything else.

Also, double check your circuit for wiring errors. That resistor between P7 and parallel RC circuit should be 220 (red red brown). Also check your program for entry errors.

Try the 1 k or 2 k resistor, sometimes the 470 discharges so quickly it's hard to see.

Sorry about all the warnings. Just make sure that negative capacitor lead is connected to Vss, and it'll be fine.

Matthew

Seems like it was a connection issue, for I did it again without changing the code and it worked.
Thanks!