FG-100 DDS Function Generator - anyone got a schematic? - Page 1
Forum section: electronics / testgear

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 16, 2014, 11:06:50 pm
content: www.ebay.com.au/itm/111146886421I bought one of these, mainly because its cheap cheap!99% of my use for it, is just for testing audio stuff, so the frequency range is more than enough.Build quality is really nice, especially for a low volume, cheap, Chinese item :pEven the hand soldering is neat and clean!And onto the question... does anyone have a schematic for this?I'm wanting to modify it, so it has a built in rechargeable battery, that I can charge using the usb cable it came with. (its either going to be a tight fit, or a low capacity)I'm also wondering what the "filter" button does?PICS!

author: onlooker
author_rank: Frequent Contributor
timestamp: August 17, 2014, 12:06:33 am
content: QuoteI could not see any usb connector on it, nor I could see enough space for a battery. Will a flat cell Li rechargeable battery fit in there?In any case, you may also not need any schematics for the portability problem, if you can use a usb power bank (<$10) placed inside or outside of the device. For this, the only thing needed is to solder the power bank in parallel to the DC input on the device. (and make sure not to use a DC supply over the rating of the power bank, which is around 5V).The worst may be that you have to rip off the small power control PCB from a usb power bank or find a similar, and, then, fit it to a flat cell Li battery if there is space for them inside.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 17, 2014, 12:19:19 am
content: It will run on 3.5 - 10volts input, and appears to step the voltage up to about 13volts, before regulating it down to 5volts for some parts of the circuit, and possibly uses the 13volts to drive the output circuit, as it can output 10volts p-p (or it may also regulate this down to 12volts somewhere)It comes with a usb to dc plug cable.Current draw at 5volts is about 300ma.I've ordered two 14650 lithium batteries, as I can fit at least one, possibly two in the case.Also ordered some protection/charge circuit boards...

author: andy_silicon
author_rank: Regular Contributor
timestamp: August 17, 2014, 04:06:31 am
content: The unit doesn't look too complex - a schematic should be easy to make within a few minutes.From your pictures and the ebay auction it has an AVR ( with a 30Mhz oscillator ).The DAC appears to be an 8bit R2R.Looking at the board and the waveforms on ebay - a switching step up regulator ( you can see the switching noise ).A hd44780 compatible lcd with backlight.A couple of opamps - one for the filter ( presumably to try and get rid of the switching noise ) and one for DC offset.So - you have the board - why not try and draw the schematic youself :-)

author: kripton2035
author_rank: Super Contributor
timestamp: August 17, 2014, 08:40:42 am
content: this one schematic should be not far from the one you bought on ebay.good digging.http://www.scienceprog.com/avr-dds-signal-generator-v10/

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: August 19, 2014, 09:53:42 pm
content: Thanks for the info guys!

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: September 22, 2014, 08:45:15 am
content: "battery low" comes on at 4.2volts... not going to work so well running it off a single li-ion cell!by the time its down to the 3.5volts they claim it to work at, it does nothing, can't get it to even turn on the output, or clean the "battery low" warning.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: September 22, 2014, 12:51:16 pm
content: its all good! seems I was getting a lot of voltage drop along the cables, low battery is actually at 3.4voltsThere's also a diode in series, which it seems I can bypass, and get another 0.8volts if needed.

author: orzel
author_rank: Regular Contributor
timestamp: October 26, 2022, 03:21:37 am
content: Quote from: kripton2035 on August 17, 2014, 08:40:42 amI doubt so. The one you link is extremely basic : does only 5V, no negative rail, no buffer output, no offset.