thread http://www.robotreviews.com/chat/viewto ... ck#p141742
A kitchen timer with stop clock function is used to measure run time of the vacuum robot to monitor aging of the battery with gradual loss of capacity. The charging dock is arranged to operate the start-stop button on the clock as the robot departs and arrives when finished. It is said batteries are worn out when down 20 per cent from original. The Powerbot lithium battery last around 400 recharge cycles. Today one would use a compact 8-pin microcontroller for this function, but I was not equipped yet to use them and was familiar with discrete logic, comparators etc.
A problem emerged with the clock never solved in the Neato version. The clock button is a conductive rubber plunger onto circuit board contact traces, connecting the 1.5v battery terminal to the circuit input. When starting, both start and stop button presses are robust as to voltage and pulse shape, but after running 30 minutes, typical cleaning time, the stop button becomes sensitive in a way where pulses reset and restart the clock, instead of just stopping. The voltage applied needs to be limited to the battery supply of the clock as many digital parts cannot tolerate inputs exceeding their power supply. However, experiments revealed the problem here is a need to slow the onset of the simulated button press voltage, using an RC delay in the connection. Some components specify a small capacitor must be used on the power supply inputs for start up conditions in which rapid onset can damage the part; no telling how the clock's chip is made. Slowed onset allows time for internal parts to adjust properly to the changing conditions.
The powerbot includes an indicator led on the dock to show connection of the robot docked. This LED is tapped with a comparator to produce a logic level output corresponding to docked/undocked condition.
A flip-flop counter isolates the time of the first run in the case where multiple recharges are made to cover the space, thereby measuring the capacity limitation of the battery, through the first, longest run in any series.
Today one might look to the smartphone apps supplied with bots to perform this monitoring, but makers have different priorities (or ignorance of the real problems using these machines). There is no support for users adding software to these apps.
Measuring the total cleaning time over several recharges might be interesting but would take a different circuit or several more components to supply both modes, and would seem best left to a software solution with a microcontroller.
The final circuit used is shown below.
Powerbot Dock with Kitchen Timer Mounted
It was interesting the BC switching transistors can switch the low 1.5v voltage of the clock's battery, with little junction voltage drop, compared to MOSFET switches usually used, which all seem to require higher voltages. For accuracy the battery itself is used to drive the button contacts instead of trying to derive from the logic circuit 5v supply.
(early version not the full circuit above; wiring is a mess of soldered jumpers on the back of the perfboard. The IC's are socketed for soldering.)