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Cheapo MP3 player update

7940 Views 71 Replies 15 Participants Last post by  Dr Morbius
Hi all,
I worked out the timer circuit for turning the player on remotely. It can be activated with any dry contact switch (mat, PIR, manual switch etc) as long as no voltage goes to the player. I'll have the circuit for turning it off in a another week or so. I'm getting the circuit drawings done as I go, and will include pics. The first timing circuit looks a bit sloppy - a couple of false starts, and I'm not the best at circuit board layouts. Progress is being made! More to come...
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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.

Before I make any suggestions, i just want to say I think what your doing is great! I don't want to come off as negative, but I have a few questions and suggestions for your circuit.

I am questioning why you have output pin 9 "sinking current" and output pin 5 "sourcing" current. Please keep in mind that the 555/556 can only sink/source up to 200mA of current when choosing your relay. The ouput pins will only go so "low" depending on how much current you "sink". It would probably be better to "source" the current in both cases.

In any case, the "sorcing" output pins will need some additional diodes. Since the relay coil is "inductive" you should place a rectifying diode (1N4001) in series with the output pin and the coil to ensure that a small 'glitch' cannot be fed back into the IC. Without this extra diode monostable circuits may re-trigger themselves as the coil is switched off. Also, a standard protection diode (1N4148) should be connected "backwards" across the the relay coil.

These additions to your circuit will avoid false triggers and preserve the life of the 556 timer.

I think I may try this myself. I can't wait for the how-to! Thanks again.
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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...
Please keep in mind that the more current that you sink, the less close the output pin will go to a low (or 0V). When sinking 10 mA, the ouput will go down to 0.1V. When sinking 100 mA, the output will only go down to 1V. They relay should still engage, but just keep that in mind. The 555/556 is much more stable when sourcing current.

Keep up the good work!
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.
Looks good Otaku. One little mistake I noticed. You have the 1N4001 diode for the bottom relay incorrect. It should be connected to pin 5. The whole purpose of the diode is to protect the IC.

Everyone better hurry up and buy those MP3 players! With this how-to they may sell like hotcakes!
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.
Very nice indeed!
I've had some requests for the final circuit layout for this project. I posted the pic on Halloween Gallery:
Let me know if you have questions. Again, mucho thanks to gmacted for the help on the fine-tuning of this circuit!
You deserve all the credit here Otaku for the great idea! I'm just glad I could help a fellow Hauntforum member.
Just curious - has anyone tried building this timer yet? If so, would you let me get your feedback as to the accuracy of the layout drawing. Also, does the how-to cover everything OK, at least up to this point? Thanks!
I plan on building one or two of these. Everything looks good to me, but I may not be the best person to ask because I know how the circuit works.
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