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[…] been a while since I exposed my students to counterfeit chips from dubious eBay channels, but now it has happened […]
Would you please specify which DS1307 chip in your photo is the genuine chip and which is the suspect counterfeit.
I have had similar DS1307 issues. The chips I got from Tayda Electronics look like the one on the right in the photo and has issues with the square wave pin enabled.
The chips I got from Futurlec, which look like the one on the left in the photo work as expected.
In my case the left one was sent to me directly from Maxim. But I have also seen working examples of the right type…
I personally had never any problems with Tayda – it’s one of my preferred sources…
Thank you for the response.
Are you certain that you have seen working examples of the right type?
Here is a detailed description of the bug I am seeing. Try enabling the 32.768KHz square wave out using a pull-up resistor on that pin, and then polling date and time with the oscillator enabled and see if you get any bus errors or frequent NACKS where there should be ACKS.
This is my first issue with any parts I have purchased from Tayda, and there has been quite a bit, but these DS1307s I got from them work only as clocks. The output oscillator is worthless because when I enable it, it only funtions alone, but then if I try other DS1307 communications such as get or set date and time there are random bus errors. Often the chip loses its time as well with the oscillator running. With the oscillator disabled, there are no errors.
Other DS1307s I have that look like the one on the left, do not have this issue even if I poll continuously with the oscillator enabled.
I will likely continue to buy from Tayda, but just as a word of caution, I have on more than one ocassion tried to communicate with them and have never gotten a response.
Just another note. I always check the square wave from these through a transistor buffer. Even the chips that I have that work very well do not like seeing any capacitance on the square wave out pin- even from a high impedance scope probe.
Also if the square wave pin is left floating (no pullup resistor), there are no errors with the oscillator enabled, but of course the floating pin is not usable output.
I have tried pullup resistor values ranging from 2.2k to 10k. No effect on the issue with resistor changes.
I have also tried other crystals for use with the correct capacitive load that the DS1307 provides internally. No effect on the issue with crystal changes.
I believe these are buggy chips. Markings below.
Tayda part number A-254 advertised as Maxim chips.
DS1307
1438A4
+102BN
Actually I have one which looks like the right type running on a clock, generating a 1s interrupt using the output pin – no problem. I have never tried a 32kHz output on that pin though on either type…
The problems I had with the chips which I identified as counterfeit where that they would lock up the I2C bus and then get hot, very hot…
If you are using the 1Hz signal to trigger an update of a date/time read then the bug I am talking about might not happen. It is most noticeable when polling more often than 250ms with the 32KHz signal enabled. Not that I normally poll that often, but the errors should not happen when I do.
Locking up the I2C bus is likely due to your driver waiting for transmissions that fail to occur. I use code that times out when waiting for transmissions so it can never block and so it can report error status codes.
As far as the heating goes, I would say that is a sure sign of a bad chip.
From now on, I will only buy DS1307s from authorized Maxim distributors. The time I wasted diagnosing the issue wasn’t worth saving a few bucks- even if it is for a personal project.
The only positive outcome in all of this is I was forced to update my TWI driver to properly handle more obscure problems than it was capable of before.
I had the experience with lots of LM2596 DC/DC converter modules… they don’t even have the switching frequency at the one specified from datasheet, and forget about ratings (they would blow up at 1/3 of expected current) not even minimum safety (failure mode is shorting input-output)(*)
If we talk about built devices then it is even more exagerated, neglecing all EMI, CE, UL… rules being even dangerous.
I keep on buying but I just don’t trust them anymore.
(*)Not difficult to guess they are counterfeits: whole module being $1 including inductor, capacitors and diode vs $2 for original chip alone…