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Step 5Smoke Test 2 - fixed resistors.
For those of you who used the resistor values in the schematic:
First, turn off S2, put a 555 chip in its socket and a 2A fuse in the fuse holder. Attach the plus circuit lead clip to the plus terminal of a 12V battery. Attach the ground lead clip of your circuit to the minus probe of a multimeter, and set the multimeter to the 10A AC scale. Briefly touch the plus probe of the meter to the minus terminal of the battery. Check for smoke. No smoke? Good! Try it for 5 seconds, then 10 seconds. Still no smoke? Great!
Check the 555. Hang a scope probe (if you have one) on pin three of the chip and check for pulses. If you don't see them then check your 555 wiring.
Next check the output stage. With the meter and circuit wired as above, turn on S2 and briefly touch the plus probe of the meter to the minus battery terminal. You should see a brief spark and hear a faint 1000 Hz tone come from the coils. The LED will turn on in the presence of output pulses. If it doesn't, but you hear the tone, the LED may be mounted backwards. If you don't hear the tone, or see smoke, then something is wrong and you'll need to check your output stage wiring.
If you heard the tone then leave the battery connected a little longer and finger test your output components to make sure they don't get too warm. If they're still only warm after 30 minutes then you're in the clear and your circuit is functioning fine. If you have a scope you can check the pulses at the chip and the output but this isn't really necessary. Your meter should be indicating something under 1.0A. If it shows more than that then you'll have to adjust the value of R2 to get the output current down.
First, turn off S2, put a 555 chip in its socket and a 2A fuse in the fuse holder. Attach the plus circuit lead clip to the plus terminal of a 12V battery. Attach the ground lead clip of your circuit to the minus probe of a multimeter, and set the multimeter to the 10A AC scale. Briefly touch the plus probe of the meter to the minus terminal of the battery. Check for smoke. No smoke? Good! Try it for 5 seconds, then 10 seconds. Still no smoke? Great!
Check the 555. Hang a scope probe (if you have one) on pin three of the chip and check for pulses. If you don't see them then check your 555 wiring.
Next check the output stage. With the meter and circuit wired as above, turn on S2 and briefly touch the plus probe of the meter to the minus battery terminal. You should see a brief spark and hear a faint 1000 Hz tone come from the coils. The LED will turn on in the presence of output pulses. If it doesn't, but you hear the tone, the LED may be mounted backwards. If you don't hear the tone, or see smoke, then something is wrong and you'll need to check your output stage wiring.
If you heard the tone then leave the battery connected a little longer and finger test your output components to make sure they don't get too warm. If they're still only warm after 30 minutes then you're in the clear and your circuit is functioning fine. If you have a scope you can check the pulses at the chip and the output but this isn't really necessary. Your meter should be indicating something under 1.0A. If it shows more than that then you'll have to adjust the value of R2 to get the output current down.
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