China frequency counter kit - not working at all - Page 1
Forum section: electronics / projects

author: bborisov567
author_rank: Regular Contributor
timestamp: June 27, 2021, 07:02:47 pm
content: So i get noting after applying power. I checked twice solder joints and the components - everything is correct. The microcontroller gets 5v power supply. On the 7550 voltage regulator output i get 3.5v (Shouldn't i get 5v?). And the weirdest thing - when i hold a screwdriver near the variable capacitor of the oscillator circuit i get random "8" (see pic) and thats all it is. Is there a way to check if the oscillator works as expected?

author: antimatter503
author_rank: Contributor
timestamp: June 27, 2021, 08:08:52 pm
content: There's not much info to go on... Can you post the schematics and other side of pcb here?General possibilities I can think of:Voltage regulator is probably loaded so much because of a short. Can you post pic of the solder side? Is the pcb touching something on your work area?Your screwdrivermight be touching ground which is touching your finger which looks like it may touch a pin of the uC as well as a diode anode and possibly other things. So you may be shorting out a pin though your finger. uC's are sensitive to that, variable caps even more so. Its pretty bad to have bare fingers up in the pcb's sensitive area.You need a non conductive poker for that sort of thing.Are you sure you did it right? Double and Triple check. To check a crystal's operation you need a scope or a freq. counter. lol the irony

author: bborisov567
author_rank: Regular Contributor
timestamp: June 27, 2021, 08:17:45 pm
content: I dont have a schematic unfortunately. The voltage regulator doenst heat up at all so i dont think there is something loading it. How can i check the oscilator, i have a scope. Just measure between the two pins? I will post a pic of the other side of the board shortly.

author: Jordanch68
author_rank: Newbie
timestamp: June 27, 2021, 09:28:46 pm
content: I would test all the diodes and transistors, one of those could be bad. The diode test function on a multimeter would be ok, or one of those cheap China ESR meters would work better. The crystal could be bad too, there's an EBay seller in the Russian Federation that sells simple crystal exciters/testers that work really well.

author: smithnerd
author_rank: Regular Contributor
timestamp: June 27, 2021, 10:22:14 pm
content: I recommend watching TheHWCave's excellent series of videos on this kit before you do anything else. You may wish to omit the poorly implemented crystal tester altogether:

author: bborisov567
author_rank: Regular Contributor
timestamp: June 27, 2021, 11:39:00 pm
content: Thanks, i will watch the videos. Meanwhile i replaced the voltage regulator with a 7805 and now a have stable 5v. Still not getting anything. Next i hooked the scope to the crystal and i get noting. Absolutely nothing. Is it possible that a brand new crystal could fail? I will try and get a replacement tomorrow and see if i get it to work.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 28, 2021, 03:01:57 am
content: Could the mcu be un-programmed by mistake ?

author: horo
author_rank: Regular Contributor
timestamp: June 28, 2021, 11:40:22 am
content: Quote from: bborisov567 on June 27, 2021, 08:17:45 pmIt's based on the DL4YHF design:https://www.qsl.net/dl4yhf/freq_counter/freq_counter.htmlA quite exact schematic can be found there:https://ssbradiogeekonair.blogspot.com/2017/12/cheap-but-effective-frequency-counter.htmlSource code:https://github.com/Ho-Ro/DL4YHF-Source-CodeSimple PIC programmer:https://github.com/Ho-Ro/ArdPicProgHTHMartin

author: bborisov567
author_rank: Regular Contributor
timestamp: June 28, 2021, 08:18:21 pm
content: Thank you for posting all of the information, definitely will be useful. I finally managed to get the device working after replacing the crystal oscillator. I also put back the 7550 regulator. To be honest i am somewhat disappointed - the frequency measurement is far from accurate and from 40 khz above it just shows zero, the oscillator tester sometimes works, sometimes it doesn't. The biggest irony is that the replaced crystal is fine when tested with the kit.This whole thing is more of a gimmick than an actual device that you can trust.

author: jxjbsd
author_rank: Regular Contributor
timestamp: June 29, 2021, 03:33:05 am
content: This is just a small toy worth 21 yuan (3.5 U.S. dollars). It doesn't even have a shell, so you can't ask for too much. If you really want to buy a reliable frequency meter from China then you need 300 yuan ($46).

author: horo
author_rank: Regular Contributor
timestamp: June 29, 2021, 07:58:26 am
content: Quote from: bborisov567 on June 28, 2021, 08:18:21 pmIf you supply the counter over the "coax" plug on the left side then the GND connection of the 3-pin header near the xtal is disconnected by the switch inside of the plug (reason: provide battery power from 3-pin and disconnect the bat if you plug in a wall wart). This took me also some time to discover why my frequency measurement didn't workThe xtal tester is (IMHO) worthless, I partially reused it to build an easy pre-amp (see also TheHWcave's video):I cannot confirm the inaccurate frequency measurement - I adjusted my counter (with my FW:https://github.com/Ho-Ro/DL4YHF-Source-Code) with the help of a GPSDO and it measures 1 MHz with (short term) accuracy of < 10 ppm.Hint: It's better to mount the variable capacitor 180° turned (contrary to the silkscreen picture). If you mount the capacitor according to the picture the bolt head is connected to the capacitor's "hot" side and a metal screwdriver will influence the frequency setting.(With my FW) I can also measure the European mains frequency of 50 Hz almost down to 1 mHz (=0.001Hz) accuracy - compared with the official values fromhttps://gridradar.net/de/wide-area-monitoring-systemorhttps://www.netzfrequenzmessung.de/.With TheHWcave's timing and display improvements the counter works up to >120 MHz - not to bad for this small piece of HW. The real ingenious ingredient is the firmware that manages the measurement and display timing completely in PIÇ assembler, invented by Wolfgang "Wolf" Büscher, DL4YHFhttp://www.qsl.net/dl4yhf/freq_counter/freq_counter.html.

author: smithnerd
author_rank: Regular Contributor
timestamp: June 29, 2021, 01:13:00 pm
content: When I built this kit, I followed TheHWCave's design for the pre-amp, in place of the crystal tester. I also swapped the adjustable capacitor for a fixed one, as that seemed like an unnecessary complication.I only use it for measuring RPM, using TheHWCave's modified FW:https://github.com/TheHWcave/PIC-freq.counter-modificationDuring testing, I didn't notice any glaring problems with accuracy, but it wasn't very important for my application.

author: neo2000
author_rank: Newbie
timestamp: May 08, 2022, 11:54:30 am
content: My kit also doesn't work out of the bag. When touching the crystal area pins there is something happening, so I removed the crystal and injected about 20MHz with my frequency gen to the left of the crystal pins. What should I say, it's working. So for me the crystal is a DOA too and I ordered another 20MHz crystal for replacement. Regards Timo

author: questore
author_rank: Newbie
timestamp: March 12, 2025, 03:18:01 pm
content: My solution was that I have resoldered the crystals legs. Nowo the crystal is now further from the board (about 3mm away) and suddenly it works.