Re: Drawdio low sound
Ah.. air-wiring SMT chips. That's always fun.
Quick suggestion: see if you can find some 28-30 gauge magnet wire.. the kind that looks like bare wire but has a thin layer of insulation baked on. It's *much* easier to work with than multi-strand wire when you build circuits this way.. especially when you're working in tight spaces.
The circuit looks more or less okay. I wasn't able to trace all the connections from the photos, but could follow enough to get the general idea. Do double-check all your pin connections to the IC.. it's amazing how easy it is to get those mixed up when they're floating in midair.
If you're getting any buzz at all from the speaker, it means the 555 oscillator is probably working, which is a good start. Just to be sure though, put it on the 'scope and check each of the pins. Pins 1 & 4 should be VCC, pin 8 should be GND and pin 5 should be 2/3 VCC. Pins 2 and 6 should show an RC charge/discharge signal running between 1/3 VCC and 2/3 VCC. Pin 7 should show a square wave between VCC and GND, and pin3 should show a square wave between VCC and VCC - .65v .
If the oscillator is working and you just aren't getting power to the speaker, there are three places I'd look: the speaker itself, the transistor, and pin 3 of the 555.
First, make sure the speaker's impedance is really 8 ohms. I couldn't see enough of it in the photos to know if that information was printed on the back. If it isn't, measure the coil resistance with an ohmmeter.. the DC resistance will be a little less than the AC impedance, but it should still come out in the 6-7 ohm range. Check the signal from the SPK+ side of the speaker just to find out what's actually happening there. From your description, I'd expect to see a low-amplitude square wave.
Second, double-check your datasheet to make sure the transistor is connected right. I'm pretty sure it is, but again, it's easy to get confused. The emitter should be tied to VCC, the collector should be tied to R2 and C2, and the base should be connected to pin3 of the 555. Check the signals at the base and collector to make sure those are right.. the base should show the same signal as pin 3, and the collector should show a square wave between GND and VCC with the opposite phase (when the base goes high, the collector goes low, and vice versa).
If the signal at the collector doesn't go from GND to VCC, it means you aren't getting enough current through the transistor, probably because the transistor can't send enough current to pin 3 of the IC. Check the datasheet for the exact chip you used and see how much current it can sink through pin 3.
If none of that leads to a solution, hopefully the information from the 'scope will give us a better idea of where to look next.
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