Maker Pro
Maker Pro

SC8560 AM/FM clock radio 50Hz drifts

M

MP

Jan 1, 1970
0
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.
2. 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 ???
 
A

Arfa Daily

Jan 1, 1970
0
MP said:
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.
2. 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 ???

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
 
M

MP

Jan 1, 1970
0
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 !!!
 
J

Jim Land

Jan 1, 1970
0
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 !!!

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.
 
MP said:
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 !!!

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
 
A

Arfa Daily

Jan 1, 1970
0
MP said:
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 !!!
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
 
Top