Some progress this will be useful for mojoe :
Here is an update on my experience in using the
mega328_st7565 firmware from Karl-Heinz Kubbeler v.1.11k on a
ebay cheap ESR meter.
When you test a diode or cap, do you get a graphic symbol in the lower right for it, or do you get the character symbol on the first line? For transistors, I get the graphic symbol. For two-terminal devices, I get the character symbol.
By the way, I've got another puzzle. I have a coil that's about 7.1 Ohm as measured with a DMM. My TT measures the resistance as 7.1 Ohm correctly. Then I insert a resistor in series to the remaining test point. It measures the resistor correctly, but suddenly thinks that the coil is about 19 Ohm!
Now for the embarrassingly-easy question (I'm new at all this). One thing I'd like to use it for is in-circuit ESR testing. So I'll need some kind of pointed probes which can also plug into the tester. Presumably into the ZIF socket. Is there anything that's recommended for that?
I'm sure this is incredibly basic, which is why it never even comes up. But I'd like to order other things I'll need, while this is being shipped. And normal multimeter probe bananas will be too fat to plug in, unless I cut their ends off. There is one version (the one with a case) which includes leads, but I don't see much discussion of them apart from that.
No, that would be too easy! It's 100 kilohm. Also tried with 500. Same result. Tried with two different testers, one with 1602 and one with 7565 display. Sometimes the coil's resistance is shown first, sometimes the other resistor's resistance is shown first, seemingly at random.
Seems to happen only with coils, but I don't have small value resistors to check at the moment.
It's supposed to have the M328 chip, on a socket. I don't know if it can take an ISP header. It has the 2-line display, which should help with firmware compatibility. It lists an 8MHz crystal.
Now for the embarrassingly-easy question (I'm new at all this). One thing I'd like to use it for is in-circuit ESR testing. So I'll need some kind of pointed probes which can also plug into the tester. Presumably into the ZIF socket. Is there anything that's recommended for that?
I'm sure this is incredibly basic, which is why it never even comes up. But I'd like to order other things I'll need, while this is being shipped. And normal multimeter probe bananas will be too fat to plug in, unless I cut their ends off. There is one version (the one with a case) which includes leads, but I don't see much discussion of them apart from that.
As I understand it, I should have an appropriate capacitor available for use during calibration. And I will need to re-read some things to better understand what would be needed to update the firmware (no idea what mine will have, but almost certainly an old version; the listing says 2013 software).
Update: The issue seems to occur if the resistance of the coil is < 10 Ohms.
Has anyone else had their tester die?
I think the ATMEGA328P in my unit died, the unit draws over 200mA when turned on and the display doesn't power on properly, the display goes to nearly full brightness when you power the unit on and then dims very low nearly instantly after.
If I may ask, since mine is apparently like yours, are there modifications that I should plan on doing to it? I don't know if this design is missing something important. ESR/capacitance checking is what I forsee for uses at the moment, for trying to help troubleshoot issues.
Has anyone else had their tester die?
I think the ATMEGA328P in my unit died, the unit draws over 200mA when turned on and the display doesn't power on properly, the display goes to nearly full brightness when you power the unit on and then dims very low nearly instantly after.Is anything getting hot on the board? If the chip is removable, remove it and power on the unit. If it behaves the same way without the chip, check the regulator and its output capacitor.
Interesting. So, if I use a low-value wirewound potentiometer and insert all three leads, it will not show the correct results? This is definitely something to be aware of.
How does your function compare to the ESR one in terms of resolution and accuracy? If he decides not to include it, I might just have to make a franken-firmware. I don't compile with UART and I enable the use of EEPROM, so should have enough memory for the modification. I'm also trying to figure out why the code for the frequency generator (function switch_frequency) is so lengthy while looking somewhat repetitive. Maybe folding it into a smaller function will free up some flash, too...
Interesting. So, if I use a low-value wirewound potentiometer and insert all three leads, it will not show the correct results? This is definitely something to be aware of.
The displayed values for the potentiometer will be fine. Only if you add an inductor of a few mH or more the tester will show the wrong resistance value for that inductor. But if you got just the inductor connected to the probes the resistance diplayed will fine again.
I removed the ATMEGA328P and the current drawn goes down to about 7 mA which seems reasonable and the display is now at full brightness but displaying gibberish as to be expected.
I think it's just a dead ATMEGA328P, but I've no idea how it died or where to get replacement firmware that's compatible with this unit.
In case anyone is interested in the graphics versions: they are described and sold within China on a Web site in Chinese only:
http://fish8840.taobao.com/ I prefer to open it in Google Chrome, which offers to translate it automatically, or on a right-click. I don't know whether the many sources of these devices buy from fish8840 (in which case they'd be all be of equal quality) or make their own copies.
Presumably fish8840 is the originator of the Chinese hardware versions (although they themselves may be imitated!), and weiweitm adapted the software. The reason for production of a graphics version given is that a text-only display in Latin characters is difficult for Chinese people, which makes sense; there are traditional and simplified Chinese, and English-language versions. There are two versions, an older one with a green display, and a later one with a slightly larger blue display; both are sold, with the blue one a little more expensive. The pictures don't show a crystal visible on the board; it could be there but hidden. As far as I can tell the later board was released in March 2014; the only software appears to be weiweitm's version 2.1 (with no mention of providing source code). I don't know if there is any provision at all for software updates (socketed chip, header, any intention to produce downloadable updates). There is a picture of an elegantly cased version, branded Yiwanjia, but no indication (such as price) that it exists.
Foreigner Markus F is acknowledged. The translation is difficult to understand in detail; I think Translate's "shelves without shell" are uncased boards!
Web pages of the two hardware versions (Chinese):
Larger screen, blue, backlit 25/3/2014, software shows as 2.1 on pictures:
http://item.taobao.com/item.htm?spm=a1z10.5.w4002-2323427594.16.IhvBUf&id=36323329572
Smaller green graphics screen version:
http://item.taobao.com/item.htm?spm=a1z10.5.w4002-2323427594.19.IhvBUf&id=37659767669
I just ordered mine, I went with this one:
http://www.ebay.com/itm/251334183807?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
...
And I will need to re-read some things to better understand what would be needed to update the firmware (no idea what mine will have, but almost certainly an old version; the listing says 2013 software).