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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 continously flickers as if counting at a very high speed. The keys to set the hour and minute appear working because the LED shows increments in the flickering itself. 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. I have also tried to put a 4.7MFG AC coupling capacitor between the transistor and SC8560 input pin.. but 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. 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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First of all download the data sheet for the SC8560. The chip is running on or about 12V, I am wondering what voltage are you running your X-tal oscillator and divider chain. I am guessing that you are using for that 5V and use the transistor to do the level shifting. If you design the circuit properly, it should work, as the 50/60Hz input has a pull up resistor, so you can drive it with an open collector circuit. The input is also a Schmidt-trigger input, so the wave form should not matter much. The data sheet shows both positive grounded and negative grounded sample circuits, make sure that you are not slipping up there. Sound card inputs are usually are AC-coupled, so it will not show correctly the DC levels. Get a proper scope with DC-coupled input, it will show right away what is wrong with your circuit.

Good luck, Peter

Reply to
Peter Orban

Are you sure you disconnected Pin13's previous connection? If that was previously coming from the AC line, you could be distorting your power supply.

Reply to
nickjohnson

-- CD4060, CD4018 Vss pins connected together. This is then connected to the Vdd i.e Pin 20 of SC8560

-- CD4060, CD4018 Vdd pins connected together. This is then connected to the Vss i.e Pin 15 of SC8560.

-- I have connected a common 33Pf capacitor across the Vdd and Vss power supply connector for the CD4060 and CD4018.

-------------------------------------

-- 1 microfarad AC coupling capacitor does not help.

-- I tried to create a low pass filter. Capacitor (1 microfarad) grounded, another pin goes to resistor ( 10K, 4.7K, 50K, 330K, 1Mohms) connected to Vdd. The common point goes to the 60Hz input of SC8560. This does not help for all the values of resistors

-- I als tried to used a BC547. Pin 13 (Q5) of CD4018 is connected to base of transistor. Collector connected to the 60Hz input of SC8560 via a 1K resistor. Emitter grounded. No Luck !!!

Huh !!!!

Looks like the harmonics frequencies in the square wave are troubling the 60Hz input block of SC8560. Looks like the schmidt trigger in there is being fooled by something spurious. How do i block that ? Creating a band pass filter that would allow only 60Hz out is very difficult ( I have limited tools here)... I am thinking to use a optoisolator... would that help to filter out those harmonics or any spurious data generated by CD4000 series ???

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

Reply to
MP

As best I can tell from a glance at the data sheet the chip multiplexes the LED display using alternate half mains cycles to drive one or the other half of the LEDs. The 50/60Hz input is needed to control this multiplex as well as to keep time.

Feeding it a time reference not synced to the mains supply isn't going to work.

If you really must make something work with this particular clock you might be able to rearrange the power supply a bit and use a couple of transistors driven from your reference clock to multiplex the display.

Reply to
nospam

"nospam"

** Well spotted.

** The OP has built himself 60 Hz a reference but lives in a 50 Hz country ( ie India).

Plus he has no doubt set the link to 60 Hz - resulting in a chaotic display.

** All gets a bit too hard just to get the time not very accurately.

....... Phil

Reply to
Phil Allison

In normal operation the AC supply is used to drive the display.

For your setup to display correctly you must produce phase and antiphase signals to drive the display.

Using a square wave drive should be fine, you just need to ensure that one half of the display is driven when the clock is positive and the other half when it's negative.

Also be sure that you have the 50/60hz clock select pin hooked up correctly.

Bye. Jasen

Reply to
jasen

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