ETEC101VPS-02 power supply USB control? - Page 1
Forum section: electronics / testgear

author: MLXXXp
author_rank: Frequent Contributor
timestamp: December 04, 2019, 01:27:35 pm
content: On a whim, I paid a few dollars for a small homemade power supply from a second hand store, without any documentation. When I opened it up, I found it contained a single board marked ETEC101VPS-02. Based on the look of the soldering and the flux left uncleaned, it's likely been hand soldered, possibly as a kit.The only thing an extensive web search turned up was anEasyEDA projectthat appears to have used the board to create a "clone" that uses surface mount parts instead of through-hole. The schematic matches the board I have.It's a straight forward LM317 design but you can switch (via an SPDT switch on J4) the lower adjustment resistance between either an external pot (on J3) or a number of resistors controlled by a PIC18F14K50 microcontroller. The PIC's USB interface is used to command it to select the resistors (through an ILQ74 optoisolator package).What I'm looking for is the USB command protocol used by this device.When connected to a PC (running Ubuntu Linux), it's detected as a USB CDC ACM device and appears as a serial port. When I use a serial terminal program to talk to it, anything I send is echoed back followed by a>prompt on a new line. Everything I've sent so far has no other effect.I've sent a private message tocarlo1300, the author of the EasyEDA project but as yet haven't received a reply.Also, the Device Descriptor parameters provided by the USB interface give:idVendor 0x2a19idProduct 0x5002iManufacturer 1 Numato Systems Pvt. Ltd.iProduct 2 ETEC101VPS_02I've contactedNumato Systems. They claim it's not a product of theirs and have no knowledge of it.If you can provide any info or ideas that might help, I'd appreciate it.Attached are some photos of the board.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 16, 2019, 03:55:36 pm
content: Pointed to this by your read pic topic I did some searching:https://www.centennialcollege.ca/programs-courses/full-time/course/electronics-lab-instrumentation-technique-etec-101/"A complete DC power supply will be built in steps throughout the course"so I guess that is where it is coming from.VPS - Variable Power Supply, I guess they borrowed the VID from Numato...

author: tunk
author_rank: Super Contributor
timestamp: December 16, 2019, 04:43:52 pm
content: I don't know about the USB commands, but isn't the heatsink a bit small?And if R3 is 390ohm, it may be a bit too high.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: December 21, 2019, 12:38:26 am
content: Sorry for the delayed reply. I either missed, or didn't get, the usual e-mails indicating that a replies had been posted in this topic.Quote from: PA0PBZ on December 16, 2019, 03:55:36 pmYou're likely right. Centennial College has campuses close to the store I bought this from. The supply board was mounted in an "off the shelf" plastic project box with the openings for the other components rather crudely cut out. Even if the supply board wasn't handmade, the case openings definitely were.I'll try to get in touch with a teacher for this course, to see if I can get some information.Thanks.Quote from: tunk on December 16, 2019, 04:43:52 pmI agree. At the 400mA rating of the transformer and set to the lowest output voltage, the LM317 would have to dissipate over 7W. Perhaps it's intentionally undersized to take advantage of the thermal overload protection in the regulator (not something I'd do), since the only other circuit protection is a 10A fuse on the 115V AC input (allowing over 1150W !).Quote from: tunk on December 16, 2019, 04:43:52 pmTrue. It's even too high for the "typical" minimum load and reference voltage ratings. I'll consider making modifications.