My name is Rajagopal 70 years old, I knows basic electronics but no experience in current programming. I have purchased a few 7 segment 4 digit with AT89C52, RTC DS1307, 74LS595 (4nos), and ULN 2003 (4nos) 12hrs format and program preloaded assembled clock PCBs. I did 12” , and 15” height and 4’ long LED display with driver circuits, this clocks are working since 2- 3 years, with Accuracy and good condition. I made a another display for another clock board, but my soldering mistake it was not work , found the fault and modified it and found working 3 digit only, the 4th digit of 10hrs digit not work, I mean, run from 0 : 0 0 to 9 : 5 9 after 9 : 5 9 it is not going to 1 0 : 0 0 instead 1 0 : 0 0 it is going again 0 : 0 0 (three digits zeros) and run up to 9 : 5 9 then again going 0 : 0 0 and run up to 3 : 5 9, after 3 : 5 9 it is going to 0 : 0 0 it mean, it is working as 10hrs + 10hrs + 4hrs for 24hrs, instead 12hrs format (12hrs + 12hrs = 24hrs). Removed DS1307 ic and replaced a new DS11307, but working as above. Not only one, few new DS1307 ics replaced but same as above. Now I doubt in 89c52, what happened changed the program code in the 89C52 it self, may it will possible?. Circuit and program are designed with AT89C52 for 12 hrs format earlier it was worked I assembled two clocks still it is working, some unknown reason RTC DS1307 is changed to 24 hrs format why?, and how to get it back to 12hrs format, may any one help me, please.
Dear all,
Now I found the problem, now it is working as usual, I did in reset pin number 9 of AT89C52 just touch a wire with 5 volt positive 3 - 4 times now it is work as 12hrs format, after (0) 9 : 5 9 it is going to 1 0 : 0 0 and as usual, I mean the 4th digit of 10hrs digit is working, I think this happen is reset problem (why, I don’t know), This circuit is already having reset circuit that is one 10mfd capacitor connected with 5 volt positive and one 10 k resistance is connected with ground. And I am having another one problem in it, that, when touch with a metal piece (forceps or naked screwdriver) in any (positive or negative) pins of any ICs in this circuit, suddenly changes going in the display digits I mean, some segments are, on or / and off (Random) its self, after fraction of seconds it is back to normal, working OK, why this happen, this circuit have connected a 100 N disc capacitor in each 74LS595 ICs vcc to with ground.
Thanks,
1) A RC reset is known to have severe issues depending on rise/fall times for the supply voltage. Or turn-off/turn-on too quickly.
2) Do you have any high-impedive inputs that you have forgotten to protect with a pull-up or pull-down resistor?
3) Are your crystal correctly mounted so the oscillator runs stable?
4) Do you connect your hardware to something else, where you might have issues with different ground potential?
5) do you have decoupling caps close (5mm) to all Vcc pins?
4) Do you connect your hardware to something else, where you might have issues with different ground potential? 5) do you have decoupling caps close (5mm) to all Vcc pins?
Dear Westermark & erik Malund,
2) No, It have 4.7 K pull up resistors. 3) I think so, now it is working ok (but few seconds are slow per day). 4) Sorry I did not understand. 5) Yes 74LS595 4 numbers ICs are having 104 pf capacitors with Vcc pins.
Thanks again.
No, I don't think they are 104 pF ?!
electronicsclub.info/capacitors.htm
www.csgnetwork.com/capcodeinfo.html
en.wikipedia.org/.../Electronic_color_code
Dear Andrew Neil,
Thanks for you point out my mistake you are correct that is not pf that is 100 N.
Thanks.
You're welcome.
Note that it's 'n' (lowercase) - not 'N'.
With the exception of 'k' (kilo; 1000), all multiples are uppercase, and sub-multiples are lowercase.
www.bipm.org/.../prefixes.html
sorry, Thanks.
Maybe there is a Nega suffix that comes somewhere after Mega, Giga, Tera, Peta, Exa, Zetta, Yotta... :p
They seem to have standardised the prefixes above exa & below atto to use complementary upper & lowercase symbols - so that would not seem to leave room for an 'N' prefix...?
But wouldn't you want to work with a project that had 100 negaohm resistors? Wouldn't that allow the voltage drop over the resistor to have a negative voltage in relation to the current direction? :)