I have a digital clock, (taken from a space heater) which is built around the T.I. M35020 clock chip which has strobed display and buttons...in this application it also takes in basic data from an LM339 from thermistors and outputs data to control relays and TRIACS for the heater...none of which I need to use.
I wish to Re-purpose it as a battery capacity measuring device for Electric Vehicle 7.2v six-cell Ni-MH batteries, where they are discharged into a 1A constant current sink and a comarator "watches" the voltage...as soon as the first cell is flat the c 300mV drop will trip the comparator, disconnect the current sink and stop the clock (but hold the number on the display), which will then read the battery capacity directly.
The clock chip has its own 400KHz ceramic resonator oscillator, but also takes in 50Hz reference from the mains. When the mains is on the 50Hz gates the strobing of the chip and is somehow locked to the 400KHz oscillator, possibly by a P.L.L. inside the chip.
I have fed other frequencies into the 50Hz input, at 10Hz, the display strobes slowly from MSB to LSB of the display and it runs five times slower...as expected. Up to 5KHz it simply strobes faster but works (at norlmal rate) only at some frequencies which presumably lock to the oscillator and at others where lock is not possible it just sort of stops randomly with one seven seg lit up. If the 400KHz oscillator is stopped it can do a multitude of things depending where in the strobing cycle it stopped and how many times the 470nF capacitor I was dabbing between the output side of the resonator and ground "bounced", sometimes it comes back with no change, but the display goes blank when the 400KHz goes, sometimes it latches up, sometomes it comes back with an advanced count.
There are at least four strobed output lines and five strobed input lines with buttons or switches at some intersections, but other intersections are ominously empty and others receive data from the 339 by some clever tomfoolery with pull up resistors to selected strobed output lines...I suspect the "stop watch" function may well lie at one of those unused intersections, but I really need the chip's datasheet for that...AND, for those who thinkGoogle Knows Everything, well not about the M35020 it doesn't!
I wish to Re-purpose it as a battery capacity measuring device for Electric Vehicle 7.2v six-cell Ni-MH batteries, where they are discharged into a 1A constant current sink and a comarator "watches" the voltage...as soon as the first cell is flat the c 300mV drop will trip the comparator, disconnect the current sink and stop the clock (but hold the number on the display), which will then read the battery capacity directly.
The clock chip has its own 400KHz ceramic resonator oscillator, but also takes in 50Hz reference from the mains. When the mains is on the 50Hz gates the strobing of the chip and is somehow locked to the 400KHz oscillator, possibly by a P.L.L. inside the chip.
I have fed other frequencies into the 50Hz input, at 10Hz, the display strobes slowly from MSB to LSB of the display and it runs five times slower...as expected. Up to 5KHz it simply strobes faster but works (at norlmal rate) only at some frequencies which presumably lock to the oscillator and at others where lock is not possible it just sort of stops randomly with one seven seg lit up. If the 400KHz oscillator is stopped it can do a multitude of things depending where in the strobing cycle it stopped and how many times the 470nF capacitor I was dabbing between the output side of the resonator and ground "bounced", sometimes it comes back with no change, but the display goes blank when the 400KHz goes, sometimes it latches up, sometomes it comes back with an advanced count.
There are at least four strobed output lines and five strobed input lines with buttons or switches at some intersections, but other intersections are ominously empty and others receive data from the 339 by some clever tomfoolery with pull up resistors to selected strobed output lines...I suspect the "stop watch" function may well lie at one of those unused intersections, but I really need the chip's datasheet for that...AND, for those who thinkGoogle Knows Everything, well not about the M35020 it doesn't!