Another FG-100 - Page 1
Forum section: electronics / beginners

author: mojoe
author_rank: Frequent Contributor
timestamp: October 07, 2025, 05:54:26 am
content: I know about all the bad ones people have posted about. I wanted something mostly for audio, that was small and portable. I have high end bench gear.I bought mine from Amazon, so I could return it if needed. The one I bought was from SeeSii, which is one of the approved sellers of the TinySA. I figured that if it was from someone reputable, the chances of getting a good one were higher. I was correct. The siggen works as it should. Even the opamps look to be authentic TI parts.The only small issue I found was that the amplitude pot didn't sit flush to the PCB, so it flexed a bit when turning the knob. An easy fix. Otherwise, it looks to be clean and well put together.I'll be attaching a battery holder for a single 18650, to make it more portable. It works just fine from one 18650. This is easier than trying to fit a pouch battery inside, and adding a charging circuit.

author: mojoe
author_rank: Frequent Contributor
timestamp: October 07, 2025, 09:42:35 am
content: I just flashed an Atmega 328P with the FG-100 alternate firmware (Google it). It has a few nice tweaks. The most useful is that after you hit "Run", it saves all your settings, so they survive a power down. No longer does the FG-100 always power on with a sine wave frequency of 100 kHz.I'll have to look at the source code, but I think it only saves the settings if they have changed. Otherwise, the EEPROM would wear quickly. Nope - it looks like the EEPROM gets written every time you press Run. What's the write endurance, 100's of thousands or more?I just noticed something important that the new firmware fixed. With the original firmware, when you powered on the device, there was a -10 VDC at the BNC connector. It went away when you pressed Run, then Stop. The next time you powered on, the -10 VDC was there again. You could blow something up without knowing why. Since the new firmware doesn't do this, it must have been due to something that was not initiallized properly in the original firmware.

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 07, 2025, 06:48:56 pm
content: FG-100, the venerable Hakko soldering iron tip thermometer?

author: BillyO
author_rank: Super Contributor
timestamp: October 08, 2025, 03:05:26 am
content: It's a cheapo function generator.

author: mojoe
author_rank: Frequent Contributor
timestamp: October 08, 2025, 04:32:32 am
content: Yes, I love my Siglent AWG, O'scope, power supply and DMM, too. The FG-100 was very inexpensive and portable. For simple sine and square waves at audio and a bit above, it works fine.As I observed in the earlier post, if you want to buy a good one, get the one that SeeSii sells on Amazon. And the alternate firmware makes it much better.I just added a cell holder for a 18650, so it's now very portable. I had to 3D print the cell holder, as every one I could find to buy is only long enough for unprotected cells.

author: BillyO
author_rank: Super Contributor
timestamp: October 08, 2025, 04:38:44 am
content: I trust SeeSii. I don't think they make anything, but they only put their name on things that do work.That one looks 100% better than the turd I picked up off AE. After a lot of repairs, both mechanical and electronic, I got it to work properly. It's not bad when it does work properly, considering the price,

author: mojoe
author_rank: Frequent Contributor
timestamp: October 08, 2025, 05:41:48 am
content: Yes, I got my TinySA Ultra from SeeSii. I don't remember, but my NanoVNA may also have come from them.

author: mojoe
author_rank: Frequent Contributor
timestamp: October 08, 2025, 05:46:20 am
content: One thing that surprised me, is the frequency accuracy. Up to about 38 kHz, it's less than 1 Hz off, and fairly stable. At the top end of 500 kHz, it's just under 14 Hz off. I have an HP counter locked to a GPSDO, so I think I can trust the readings :-)