Maynuo M9812 USB Question (and mainboard photo) - Page 1
Forum section: electronics / testgear

author: synapsis
author_rank: Regular Contributor
timestamp: September 28, 2013, 04:39:14 am
content: My Maynuo M9812 300W DC Load arrived today. Unfortunately, the required USB -> Serial device didn't come in the box. Does anyone have any information on the device? Maybe an idea of what's in it? I'm guessing it's an optically isolated RS232 -> TTL serial convertor.The C8051F340 MCU that it uses has USB capability, so why the extra requirement?I'm including a photo of the mainboard since I had my camera equipment out already when it arrived. This is a reduction from the 177 megapixel original. Notice the model number (MN9711) in the lower right corner. This board needs a bath.

author: synapsis
author_rank: Regular Contributor
timestamp: September 28, 2013, 05:45:48 am
content: Ok, answering my own question for the sake of anyone else who wants the info. It's just TTL Serial.I found the answer in the manual on page 44, after I rang out the tracks on the board.The DB9 on the back of the unit is:Pin 1 - 5V, connects to the REGIN pin on the MCU.Pin 2 - Receive, connects to P1.6 on the MCU.Pin 3 - Send, connects to P1.5 on the MCU.Pin 4 - NCPin 5 - GroundPin 6-9 - NC

author: H.O
author_rank: Frequent Contributor
timestamp: September 28, 2013, 01:48:26 pm
content: Yes, the port on the unit is logic level serial and the dongles you can buy from Maynuo are indeed isolated. I've got the M-131 (RS232) one, I can probably open it up if you want me to.

author: crt
author_rank: Regular Contributor
timestamp: September 28, 2013, 02:33:55 pm
content: I have M-133 (USB)its very easy to teardown it, but i see 2 IC that have number been erased

author: synapsis
author_rank: Regular Contributor
timestamp: September 28, 2013, 06:03:03 pm
content: If it wouldn't be too much trouble, could someone post a photo of the board (either 131 or 133)?It took almost a month for the M9812 to get to me from China, I can probably build an interface from spare parts before one could get here from China.

author: H.O
author_rank: Frequent Contributor
timestamp: September 28, 2013, 08:40:53 pm
content: No trouble, attached is shot of the M-131.The instrument connects on the right hand side, PC on the left hand side.As in crt's unit the IC markings have been scraped off but it's pretty clear that the narrow SO16 package is a MAX232 or MAX202. The wide SO16 is an Analog Devices part (the logo is 80% visible), most likely one of their ADUM series digital isolators.They are clearly "stealing" power from the COM-port to power the MAX232 or whatver chip it actually is. If you want USB, slapping a FTDI FT232 and an ADUM2201 or simmilar together will most likely do it.Looking at the photo, C6 and Q2 doesn't look to be in very good shape but the thing does work.

author: synapsis
author_rank: Regular Contributor
timestamp: September 28, 2013, 09:37:47 pm
content: Excellent. That helps a lot.Thanks!

author: mcinque
author_rank: Unknown
timestamp: September 28, 2013, 10:03:31 pm
content: Quote from: synapsis on September 28, 2013, 04:39:14 amForgive my OT, but damn, that board needs a big washing cycle.I was expecting more quality at that price.

author: synapsis
author_rank: Regular Contributor
timestamp: October 16, 2013, 07:42:30 pm
content: For reference of anyone else who needs an isolator, here's what I came up with. It plugs straight into the Maynuo load, and into the computer's USB port. It's isolated and works at 115200 bps.I'm a programmer and not a hardware guy, so improvements are always welcome.

author: casinada
author_rank: Frequent Contributor
timestamp: October 16, 2013, 10:10:03 pm
content: That looks very good for a home cooked PCB

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: October 17, 2013, 02:39:36 am
content: VCCIO of FT232RL must be connected and it is not connected. I am pretty sure if VCCIO is not connected to +5V or +3.3V it won't work.

author: synapsis
author_rank: Regular Contributor
timestamp: October 17, 2013, 03:34:21 am
content: Quote from: Alexei.Polkhanov on October 17, 2013, 02:39:36 amYou're right, VCCIO isn't connected and it should be. I totally missed that. The odd thing is that it works and communicates.Updated schematic:

author: LaurenceW
author_rank: Frequent Contributor
timestamp: October 17, 2013, 05:17:55 pm
content: Yes, that looks good. So much for rubbin' off the logos, eh?! Never seen that ADuM2402 chip, before. Very interesting...I've got a Maynuo and a RS232 version of the isolating lead. For a while, I suspected that this was broken, so manage to rig up an (unisolated) replacement with just simple TTL>232 level converters. It worked fine. The isolating lead does no more than that - electrically isolate the signals at either end of the cable. This may be IMPORTANT because the serial connections at the back of the eLoad are connected to the -ve load input terminal, which of coursemightbe +/- many volts from equipment ground! Fzzt...

author: casinada
author_rank: Frequent Contributor
timestamp: November 20, 2013, 06:25:25 am
content: Probably the ADUM chip knows how to steal power from the send and receive signals