1/8 inch 4-contact phono jack to USB pinout? - Page 1
Forum section: electronics / beginners

author: edy
author_rank: Super Contributor
timestamp: July 20, 2014, 06:14:52 am
content: Hi folks, I was hoping someone could help me figure this out. I have an MPIO player with only 1 jack (1/8 inch phone with 4 contact type it seems) which was designed to also allow charging of the battery. That is the only port on the device. Somehow it connects to USB to get charged but I don't know the pin outs and I don't have a cable/dongle/adapter. I've linked some images I took or gathered from the net... one shows a pin out but I am not clear what it means. I see 4 contacts on the phono plug but USB has 2 power, 2 data and a ground... do I just ignore the ground? Thanks! by the way, is this some standard or just used on some MP3 players?

author: edy
author_rank: Super Contributor
timestamp: July 20, 2014, 06:21:27 am
content: I found this file... looks like anything goes... Do I just try to make a cable and see what happens? any chance of frying the player if I have the power polarity reversed? Or the data pins flipped?Notice the image here shows usb data negative on the tip end, but the one with Chinese letters previously says DP for tip which is I assume data positive and the other DM for data minus? There is a discrepancy and I am not sure if I am looking at the male end or female end of USB and order of the pins.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 20, 2014, 06:43:33 am
content: Quote from: edy on July 20, 2014, 06:21:27 amNO! That diagram indicates that there are several "standards". And you must select the correct one, or you will surely toast your MP3 player gadget.QuoteNO! Unless you were going to throw away that gadget anyway.QuoteYES ABSOLUTELY! If you get this backwards, its all over, toss it in the bin.QuoteThe device probably won't communicate with the data pins flipped, but it probably won't smoke it.You could either trace out the wiring between the battery and the connector to determine the pinout, or else insert a TRRS plug into your gadget and probe it with a meter to see if you can find any residual battery voltage (to indicate power polarity).IMHO, after you get the power connections right. You can try the data leads both ways and see which way works.

author: edy
author_rank: Super Contributor
timestamp: July 20, 2014, 01:10:52 pm
content: Thanks for the advice. I will see if I have a 4-contact jack somewhere... otherwise I can solder on a couple of wires to the board where I can tap the proper contacts and wire a USB port to it. I could have a separate USB port and still use the phono jack with regular 3-contact earphones... I am not interested in restoring the device to original condition so I don't mind hacking it this way. Hopefully I'll find a 4-contact plug in my junk drawer. I thought these devices have polarity protection like a diode that can handle 5v reverse but I shouldn't assume, since the design doesn't really give the user choice so there should never be a reason for reverse polarity and they probably didn't build in any protection. I assume it works by detecting 5v on the base of the plug and switches the function to USB, and when it doesn't detect 5v it switches the port to a phono audio jack... if I get it reversed it may keep the jack in phono mode and blow out the audio amp circuit.

author: SeanB
author_rank: Super Contributor
timestamp: July 20, 2014, 02:14:07 pm
content: Most cellphone headsets that you get free with the phone are 4 pin plugs, and came with a short cable already attached. You just have to measure which wire goes where.

author: edy
author_rank: Super Contributor
timestamp: July 21, 2014, 12:14:52 pm
content: I found a 4-contact headset in my stash of parts but before I used the wire cutter on them I noticed some other problems with the MPIO, so I didn't want to sacrifice a good headset for nothing. The LCD display was lifted up on the end which has LED backlight... turns out the LED contacts separated from the PCB, taking the copper layer area with it! The only way to solder it back on was to scratch my way through adjacent solder mask to get back to the copper trace underneath, since trying to normally solder wouldn't stick to anything. By the time I finally did that, it kept separating, I just powered the LED separately from an external supply. I got it powered up but it kept complaining about low battery... I tried charging it for a while, still complained. So I took out the battery (looks like single cell 3.7v lipo) and powered it directly by external supply as well... and it still displayed "low battery" and would shut off. So after an hour or more wasted, I threw the whole thing in the trash. Date codes on it were 2004-2005 or thereabouts. Just not worth the time, there was nothing on it of importance!