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SC8560 AM/FM clock radio 50Hz drifts

Hi, I have been struggling on this for almost 2 weeks and I hope someone can help me.

I have a Duraband AM/FM digital alarm clock radio. It work on SC8560 which takes either 50Hz or 60Hz line input for frequency reference. Unfortunately, my power line frequency is not stable and drifts from

48.5 to 50hz results in my clock slowing down be few minutes every day. So I am using a 2.45760 Mhz crystal, Divide by 4096 using CD4060 to generate 600Hz and then divide by 10 using CD4018. The 600Hz and 60Hz waveforms are generated neatly.

However, when i connect the 60Hz i.e. Pin13 (Q5) of CD4018 to the

50/60Hz input pin of SC8560, the entire LED display freezes and shows 1P:G8 All the keys to set the hour and time also freeze... Can some one please help ?

  1. I have used BC547 to drive the output of CD4018 and then connect the collector to the SC8560 but it does not help.

  1. I am using the same powersupply for the 8650 and CD4060/18. It seems that 8650 works on negative voltage. ( I doubt that my problem is to do something with this.. but not sure what !!!)

There are few more problems that i face

  1. The CD4060 does starts oscillations only after 20sec of power on. I am not able to figure out a reason for the same.
  2. I am trying to use the shareware software zelscope to view the waveforms on my laptop using the sound card as input probe. In the frequency view, the 600Hz waveform appears neatly, but the when i divide it by 10, the software shows it as 64.6Hz instead of 60Hz. Is this a software error, noise in the probe, line humming disturbance etc or is it really NOT 60Hz ???
Reply to
MP
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Have you tried AC coupling the 60Hz signal to the '8560 using say 1uF polyester from the collector of your buffer transistor ? As far as the PC reading the final frequency at 64.6Hz, I would suggest that this is more likely to be a reading error than a real one. Any such software depends heavily on such things as how accurate the sampling frequency of the soundcard is. Where it is on-board, as in the case of a laptop, I wouldn't trust it to be very good. Also, other background tasks can steal processing time which can lead to inacuracies in such measurements. Remember that you are dividing down by a total of 40960, so any error in the final count would have to be 40960 times that error at the original oscillator, in this case

188.416kHz. That would be a long way for a 2.4 meg xtal to be off its frequency. Do you have the facilities to measure the clock generator's freq just to be sure ?

Arfa

Reply to
Arfa Daily

Hi Thanks. I tried to connect a 4.7MFD capacitor. Not much help... the LED display continues to blink/flicker as if it is counting in a ultra fast mode.... today, the keys for hours and minute setting are working and i find that even in the blinking, the decimals are being incremented. Yesterday, the keys were frozen because i guess the oscilloscope probe was connected to the collector of the transistor....

Since the LED's are counting very fast, i feel that the SC8560 is looking at the harmonics too... but the documentation says that there is a schmidt trigger inside... so this should have been taken care of... !!!

Is it that the SC8560 does not like square wave at all ? and needs to have a sine wave at its input ? I dont think so, but this is just a wild guess !!!

Arfa Daily wrote:

Reply to
MP

"MP" wrote in news:1166681755.011742.70830 @i12g2000cwa.googlegroups.com:

Good thought! Try a low-pass filter to get rid of ringing or spikes (what you call harmonics) and just give the schmidt trigger a smoothly- rising and falling waveform at 60 Hz to trigger from.

Low-pass filter: series resistor, capacitor to ground. Take the output from the junction of the resistor and capacitor. Try something like a 4k resistor and a 1 microfarad cap and see what happens.

Reply to
Jim Land

If you scope the original 50Hz signal, then scope the point with your

60Hz source connected, what difference do you see?

If you dont have a scope, theres free pc scope software that will do that quite happily.

NT

Reply to
meow2222

That was going to be my next suggestion, and the same thing to try as Jim says below with putting a low pass filter in the path. I doubt also that it

*needs* to be an actual sine wave, but maybe floating, hence my suggestion of a series cap, which I would feel inclined to keep in after the LPF, and with a slow slew rate, like a sine wave, which will be created by the LPF.

Probably will end up more like a rough sawtooth thana sine wave. That said, it is a Schmitt input for a reason, and that reason is probably that it is expecting to be fed by a sample of the line input voltage, so may be critical for waveshape.

Simple counters using 4000 series CMOS, can often generate switching artifacts in their output waveforms, which might only be a few nS wide - certainly not wide enough for your PC based scope to see, and even a challenge for a good quality professional workshop scope, but certainly enough for a Schmitt input to see.

Arfa

Reply to
Arfa Daily

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