Thanks, I found some LM2900's. My initial Google quick search for LM3900's turned up comments on their unavailbility.

Ed.

The OP275 is a nice opamp but isn't characterized for operation under +-4.5V (9V total).

Good point about the 5 volt single supply. When I tossed this thing together, I initially tested it from a separate supply and wasn't terribly concerned about the supply voltage. It was running at about 10 volts. So, I went back and confirmed that it does operate properly from a single 5 volt supply. Since the LM3900 output swings between 0.1 volt and Vcc-1 volts, that gives a 3.9 Vpp swing from a 5 volt supply, in which case it's a good idea to bias the output to about 2 volts rather than 2.5 volts. So, the 680k resistors should be replaced with 1 Meg. resistors when powered from 5 volts. (It was working fine with the 680k bias resistors at 5 volts, but 1 Meg. resistors should guarantee a little more output swing before clipping.)

I was doing a bit of guessing you intended a single 5V supply but one could also do a double supply, like you did for testing. That isn't necessary to simply shape the same output level, and a single 5V supply is simpler, but if that MP3 output is low for the transmitter you could use the opamp to gain it up as well, in which case you'd need a higher voltage to accommodate the larger swing.

Bob, I ordered one when you first posted and received it today.



Where is the spec sheet for this? 3.7 Volts?

I ordered one around the same time too
Jan 28th
... but have not heard a word about it since.

Was wondering what's going on.

Looks as if it may have been temporarily out of stock. Hopefully, they're shipping again.

Mike,
It will work on any voltage between 3.7 and 5 volts.

I never found a datasheet for this exact unit, but I did find a schematic for another one that uses the same chips and was close enough that I was able to figure out the important features. I'll dig it out and post the info shortly.

I ordered two Jan 17 and had them before the end of January. I run them on 5 volts and they work very well through the little circuit that Bob designed. Even works well through the phono input of my Victor RE-45.

Ed

Here is a collection of notes that I compiled while tinkering with this thing:
http://electronbunker.ca/DL/MP3_Player_Notes.pdf

Is this real?

Yes and no. The 12 volt power option requires that you add a voltage regulator IC to the board. It would mount on the big square foil pad between the electrolytic, and the clock crystal. So, as it is, you can't use it on 12 volts.

So I guess that's why you loose the time setting when it's shut off... right.
Or am I over-stating the obvious.. if so sorry

Seems to me that the RED BATT plug was meant to be connected primarily to a battery back-up only for that reason.
The 12V in ( with a regulator added to the board LM7805?) would have been the normal power in.. and so ...if a BATT was connected to the RED plug ...the time wouldn't be lost.. right?

If so... are the other regulator parts already on board now.. so you only add a Lm7805? or LM317? .. or what?

Originally, I thought that the red battery plug was for the clock too. But there's a power switch on the front of the unit, and when it's switched off, it disconnects the red connector and it kills the clock. So, if there is a means to keep the clock going, it would have to be connected somewhere else. I'm beginning to suspect that the clock function just happens to be part of the main controller chip, but hasn't been properly implemented on this particular circuit board. Though, it may be possible to find some other point to connect a backup battery.

I'm impressed. This player has enough power to drive two large speakers.

How tough is it? I'm using this with a 6V supply. Because the 7805 needs 2V difference, I'll use three diodes to drop 2V. (Four new alkaline batteries could supply almost 7V.) As the batteries discharge, say to 5V, will the player quit at 3.7V?

I think 6 volts is pushing it a bit. Most of these logic circuits don't like anything any higher than 5.5 volts max.

When I first got mine going, I was powering it from 3 AAA batteries, so it was about 4.5 volts. When the batteries started to get weak, it was cutting out around 3.5 volts. Now, I'm using a 5 volt wallwart that's designed for running USB powered devices.

That's what I used and was happy. Install in in a portable radio and the voltage drops quickly with 4 "C" cells. A quick check, it drew 120mA.

What are these board connectors called? I want to get some matching plugs but not familiar with the terminology.



Thanks
-Sam T.

Not sure but they look like they might be a variety of "MOLEX" brand connector.... maybe the "P4-MB" ?

If anyone has found a source for these plugs, please post a link..I went all over looking for them at R/S and computer stores...no luck. Even the google search has not found anything this small. yet.

Dale

I can't really answer the question but I think those connectors are the same 'type' as found on sound cards, except those are 4 pin vs the 2 pin versions they're using.

I just thinking that if you can find the ones used on sounds cards that might give you a product line to search in for the 3 pin version.