Cheapo MP3 player update

This one:
http://www.mpja.com/category/Unique_Items/MP3_PLAYER_16520_MI.asp

For $5 it's a pretty good deal, but you have to buy three of them to meet the minimum order.

In a way. Right now, I'm planning to use a second timer circuit to control the power to the player. Both timers will start at the same time, but one stops after starting the player (~1.5 sec). The other timer stays on for the duration of the file, and will be controlled by a potentiometer. This means that you need to know the length of the file, and you'd need to play with the timer a bit to "dial in" the pot. Adding a short silence period at the end of the file will help in preventing restarts. I'm still trying to determine a way to monitor the playback IC so that it can be shut down at the end of the file, but can't find any info on the chip. I suspect that it has proprietary firmware in it as well.

Whew! OK, I built and tested a 556 timer circuit that lets me turn on the MP3 player, play the file once, and shut down the power supply to the player when the file is finished playing. The next trigger event starts the whole thing over again. This circuit is pretty much a prototype, so is a bit messy. I also plan to use a different board (easier to use) for the next builds, so I'll start the how-to picture fest when I get the new parts. The bottom line is that one can now turn these players on and off remotely, with the event controller of your choice.

These players have very good sound quality, and you get the bonus of stereo tracks. The ISD chips in the Scary Terry boards can only record mono. They hold several minutes of sound, depending on the bitrate used in the file (Dennis at Wolfstone estimates that at certain rates, the player will hold ~30 mins). For $5 each they're hard to beat, especially if you're planning a looping soundtrack.

It'll take a couple of weeks to get a good how-to together for this hack. I'm still in the R&D stage, and am looking for the best board to make the timer assembly easy. The concept is proven, however, and I just need a solid parts list. I'm trying to single-source all the parts. I have the circuit drawing, but its in a .doc format so I can't attach it to a post. If anyone wants a copy, PM me and I'll email to you. Please note that I may be changing the values of the 470 uF cap and the 1 MOhm pot - I'm still experimenting with this part.

OK, I have the circuit worked out. The values of the 1 Meg potentiometer, the 1K resistor and the 470 uF cap can be varied to change the timing period. I'm still working out the how-to, but here's a drawing of the circuit. The remainder of the circuit that connects the relays to the USB connector and the MP3 play button are in the works and I'll post it soon.

gmacted,
Thanks for the suggestions. I had seen the use of the diodes on some circuit drawings, and was thinking about doing that myself. As regards pins 5 & 9, the wiring is as found on several circuit examples I looked up on the web. I am paying attention to the current requirements of the relays I'm choosing, and will keep the coil current demand low (< 100 mA). More to come...

Here's the latest revision of the timer circuit. I still have to draw the power connections to the USB connector and the player start button wiring. Many thanks to gmacted for his valuable advice on the addition of protection diodes. I'll try to get a pic of the start button wiring up later today.

Thanks, gmacted. I fixed the error in this drawing. Please note the solder locations on the MP3 module's play button - I found these to work for starting the player, but they're very small surface-mount pads. Use a small solder tip and 30 gauge wire. I plan to use a 2-pin Molex connector to attach these wires to the circuit board. You need to be able to disconnect it to upload files.

Oooops! The software dropped a line where it didn't belong - here's the corrected version. Note: the MP3 player is shown with the case opened.

I've almost finished the parts list for the circuit. Almost everything you need is at All Electronics. The hardest part to get is the USB-A female connector. Jameco has them (p/n 161023, 0.79 ea.), but you get stuck for shipping one part. What I did was to request free samples from Keystone Electronics.
http://www.keyelco.com/products/specs/spec141.asp
Click on the sample link and make up some info about your "company" and how many you plan to buy each year (at least 1000), and they'll send them to you for free. I got 10 of them, but they did email me saying that this was more than they usually send for sampling. Try for 4-5 and you'll be OK.
I want to post a decent how-to for the assembly of the board, so it's going to take a little while. I want to get lots of pics as I go along.

Circuit map

I made a layout drawing of the circuit to make it easier to see where everything goes. It's based on a PC-3 board available from All Electronics. All questions and feedback are welcome!

Actually, I did think about doing it that way. You could tap into the battery terminals in the case and wire Relay A to control the power, it just needs another Molex or similar connector. I just liked the ease of plugging the MP3 module into the board.

I'm expecting the parts for this hack to arrive next week, at which time I'll start the how-to. There's going to be lots of pictures and text, and trying to post these will run me out of attachment space real quick. Is anyone interested in hosting the how-to on their web site?

Thanks, bourno! Let me know what formats you'd need for the pix and text instructions and how to get them to you - the parts are on the way.

Yes, the final circuit layout is on my post dated 1/19/07. I don't know how to link to a thread or post.

For those who will be building this circuit, go to R/S and get a spool of bus wire:
http://www.radioshack.com/product/i...&cp=2032058.2032227.2032239&parentPage=family
It will make the bus bar layouts way easier, as you won't need to strip wire.

I'm putting the first board together and taking pix as I go. After I finish the first one and test it, I'll post a parts list. More to come...

Looks good, bourno! Is the Prop-1 able to detect the end of the MP3 file to prevent replays? That's the biggest hurdle I ran into - nobody seems to be able to find any info on the player's controller chip. I did find a datasheet on the MP3 decoding chip, but none of the output pins had anything useful for detecting end-of-file.

The pause between replays is ~ 0.5 sec, according to my 'scope. Of course, if one adds a few secs of silence at the end of the file, it gets easier to hit that target. True, you would have to recode the pause or relay-off for each change in the file length. The 556 circuit allows setting time periods on the fly.