Audio generator device thingy - Page 1
Forum section: electronics / beginners

author: soldar
author_rank: Super Contributor
timestamp: March 02, 2024, 03:41:16 pm
content: I couldn't think of a more descriptive title. I bought on eBay some of these devices, for lack of a better word, with the intention of using them maybe for something like have a loudspeaker make the sound of a barking dog when triggered by some alarm , PIR or whatever.I have no information other than what is shown in the attached image. I cannot seem to get anything out. Before I spend more effort I'd like to ask if anyone has information, experience, ideas, advice, or whatever.

author: jwet
author_rank: Frequent Contributor
timestamp: March 02, 2024, 03:52:33 pm
content: You're missing a resistor/your diagram is wrong. The resistor value is not critical, kind of a pullup. 10k to 400k works.

author: soldar
author_rank: Super Contributor
timestamp: March 02, 2024, 04:37:52 pm
content: Quote from: jwet on March 02, 2024, 03:52:33 pmAh, thanks. I'll give it a try. Do you have experience with these? What kind of output level can I expect? I am thinking I will need an amplifier after this. Right?

author: Benta
author_rank: Super Contributor
timestamp: March 02, 2024, 07:18:13 pm
content: Is it one of those things from a musical greeting card?They normally use a piezo speaker with significantly higher impedance than 8 ohmx.

author: soldar
author_rank: Super Contributor
timestamp: March 02, 2024, 08:07:16 pm
content: Quote from: Benta on March 02, 2024, 07:18:13 pmThat's what I am thinking. I will probably need an amplifier with high impedance input. I guess I will probably have to figure it out myself.

author: jwet
author_rank: Frequent Contributor
timestamp: March 02, 2024, 10:16:02 pm
content: I played with them long ago with a niece that got them somewhere- she had them hooked across everything. They were sold by a Novelty Store in the US for a while- they probably bought from China. The end product was a little door bell alarm that made a barking sound. It worked pretty good.

author: soldar
author_rank: Super Contributor
timestamp: March 24, 2024, 07:26:33 pm
content: I've been playing a bit but I am not getting good results. I am thinking the output is probably an H bridge and designed to be connected directly to a piezo speaker and does not interface well with a following amplifier. The barking sounds I managed to hear were quite distorted and, in any case, I do not think would fool anyone into believing there was a real dog. I think I am giving up.

author: Zero999
author_rank: Super Contributor
timestamp: March 24, 2024, 08:27:30 pm
content: Don't give up too soon.I can't say for sure about the IC shown in the original post, but I have seem similar boards in toys which drive a small 8 Ohm speaker. A speaker is normally used when a piezo transducer doesn't have sufficient frequency response. It's normally a crappy plastic speaker about 25mm or 30mm in diameter, but a larger 8 Ohm speaker will work and sound much better. An efficient reflex horn, designed for PA and security alarm applications might even be quite loud.Have you looked at the output on an oscilloscope? I suspect it's a class-D PWM output stage. If you want to drive a larger speaker, you could try a couple of MOSFET drivers, connected to suitable MOSFETs, running at a higher voltage of course, with the chip powered from 3V. You might need to add a small filter to cut down on RFI and reduce the power consumtion.

author: soldar
author_rank: Super Contributor
timestamp: March 24, 2024, 10:09:12 pm
content: Quote from: Zero999 on March 24, 2024, 08:27:30 pmI had not thought that it might be a class D but now that you mention it I think you are probably right. I did a quick setup and the power supply was acting funny and I did not feel like looking into it any more but it makes sense. The power supply was set at something like 3.8 V but the voltage would drop when activated, like it was pulling current and the current limiter was active but it didn't make sense and I didn't feel like looking into it. Now it makes sense that the device was demanding higher frequency. Maybe a capacitor would help. I will have to look into it. Thanks for your observation!