hi
ive built the mk 151 it works perfectly,and looks great,ive changed it to blue led display. however i would like to use it in my car,unfortunately it then goes a bit haywire, losing a 1/4 of an hour a day sometimes,
i suspect that although the memory uses the 4.5 volt batterywhich should be stable,the clock is being affected by the car battery/starter circuit, which supplies the power.
any thoughts
dougal
The unit has been designed to mainly run from an AC source.
Most likely, the 12V which is fed to the MK151 is not very smooth, so spikes fool the unit and make it think it runs from AC every now and then.
When there is no AC, the unit switches to a (less accurate) internal oscillator. Every time it switches between AC sync and internal oscillator, its internal timing gets disturbed, this explains why it looses time.
You will have to provide a very smooth 12VDC, e.g. by adding a diode and a large (4700µF) cap in the supply line.
Even then, the unit will run from its internal clock, which is a 20ppm clock (2-3minutes/month accuracy).
thank you, im impressed, i expected to be told it couldnt be done.i did add a capacitor across the input. which certainly helped, but it was not a large one
where would the diode go?
thank you again
doug
http://s1353.beta.photobucket.com/user/dougalere/media/DSCF0003.jpg.html
ive got it, i think,- the diode would block any AC component?
regards
doug
The diode would have to go in series with the positive supply, before the cap.
Please note that these hints are based on assumption, this has not been tested.