Timer with monitor

Hi invitech - if I was doing this I would use discrete components, where the word 'discrete' includes relatively simple LSI and MSI digital integrated circuits. However you go about it you will need a clock signal. If the unit is mains-powered you could obtain 50Hz square waves using a small isolating transformer to drop the mains voltage down from 230v to 3v AC, and a simple comparator chip to turn the resultant sine waves into square waves of about 5v peak-to-peak. Ideally you need an oscilloscope to check the volage of the 5v p-p from the transformer before connecting it to the comparator. Watch out for those mains voltages, they can be lethal. The output of the clock circuit can be connected via an AND gate (see below) to the CLK input of a suitable programmable counter chip that will count up to the maximum value required. This will depend on the battery capacity and how much current you will be pushing through it on charge, or the amount you will be draining from it during discharge. The outputs from the counter chip will go to a chip that converts a digital value to the pattern required to drive a 7-segment multi-digit display. A 'Stop/Go' switch will be needed, when it is in the 'Stop' position the RST pin on the counter needs to be held in the RESET state. When you switch to 'Go' the RST pin will change state and allow counting to start from zero.

Waiting in the wings will be another comparator. One input will be monitoring the battery voltage, the other will be monitoring the voltage from a suitable 28 VDC reference supply. This will need scaling down to suit the max input to the comparator. The design of the reference supply depends on how accurate you want it to be. I found that band-gap references did the job. You will need to scale down the 28VDC from the battery to match.

One input of the AND gate (see above) will be connected to the scaled-down 28VDC from the battery, the other input to this gate will come from the clock circuit. By this means the clock will stop when the battery voltage reaches 28V DC.

Measuring discharge time follows much the same system. You'll need a 16VDC reference, and an inverter on the battery-voltage signal to the second comparator so that counting starts at anything higher than 18V and stops when it gets down to 16V DC.

Sorry the above is a bit sketchy in places, it's been a long day... 

Hi invitech - if I was doing this I would use discrete components, where the word 'discrete' includes relatively simple LSI and MSI digital integrated circuits. However you go about it you will need a clock signal. If the unit is mains-powered you could obtain 50Hz square waves using a small isolating transformer to drop the mains voltage down from 230v to 3v AC, and a simple comparator chip to turn the resultant sine waves into square waves of about 5v peak-to-peak. Ideally you need an oscilloscope to check the volage of the 5v p-p from the transformer before connecting it to the comparator. Watch out for those mains voltages, they can be lethal. The output of the clock circuit can be connected via an AND gate (see below) to the CLK input of a suitable programmable counter chip that will count up to the maximum value required. This will depend on the battery capacity and how much current you will be pushing through it on charge, or the amount you will be draining from it during discharge. The outputs from the counter chip will go to a chip that converts a digital value to the pattern required to drive a 7-segment multi-digit display. A 'Stop/Go' switch will be needed, when it is in the 'Stop' position the RST pin on the counter needs to be held in the RESET state. When you switch to 'Go' the RST pin will change state and allow counting to start from zero.

Waiting in the wings will be another comparator. One input will be monitoring the battery voltage, the other will be monitoring the voltage from a suitable 28 VDC reference supply. This will need scaling down to suit the max input to the comparator. The design of the reference supply depends on how accurate you want it to be. I found that band-gap references did the job. You will need to scale down the 28VDC from the battery to match.

One input of the AND gate (see above) will be connected to the scaled-down 28VDC from the battery, the other input to this gate will come from the clock circuit. By this means the clock will stop when the battery voltage reaches 28V DC.

Measuring discharge time follows much the same system. You'll need a 16VDC reference, and an inverter on the battery-voltage signal to the second comparator so that counting starts at anything higher than 18V and stops when it gets down to 16V DC.

Sorry the above is a bit sketchy in places, it's been a long day...