Got sick of the infamous battery ritual to
reset the CM15A. So I installed a normally
closed pushbutton on the case and wired it in
series with U5. When pushed, it interrupts
power to the 5 volt regulator and resets the
controller. You dont even have to unplug it!
Joe
GREAT idea BUT......
The regulator in the CM15 is a LM2931 (a LDOV (low drop out voltage)) regulator so that it will still operate when the battery voltage gets to around 5 volts.
THIS IS A PROBLEM with this CHOICE of regulator because under NORMAL load, the unregulated input voltage is about 24 volts (after the bridge / zener / 150ohm resistor) at C12.
When the input (or output for that matter) to/from the regulator is removed, the UNregulated voltage rises to about 34-37 volts (depends on your AC input voltage).
When the power is reapplied to the regulator, it shuts down because of the over voltage shutdown (protection feature) of the regulator. Linear Tech's data sheet lists this value as "Maximum operational input voltage".
The data sheet for the regulator (search for LM2931) states that it will shut down if the input voltage exceeds (typically) 33 volts, and this is exactly what happens when the load is removed from the regulator's input!
I would imagine THIS IS WHAT IS "HANGING" (as what alot of people have problems with) the CM15!!
Think of this scenerio: 1) Everything is running fine and your AC line is a little bit high on the line the CM15 is plugged into because some heavy loads (Uwave, AC, coffee maker, clothes iron, electric floor heater) are running on the OTHER line and the loads on the AC lines are not balanced and the neutral has been pulled to the loaded side that makes the line to neutral voltage for your CM15 a little higher than 115 VAC. Could be as high as 125-128 volts!!!!
2) An inductive load is applied across one of the heavily loaded lines and creates a small spike that walks through the PS transformer/FWB/filter caps/zener/150 ohm resistor, and spikes the 28-30 UNregulated voltage to around 33-35 volts.
3) The LM2931's crowbar circuit shuts down the regulated 5 volts and the CM15 seems to "hang".
it is REALLY SHUT DOWN!!!! The ONLY way to recover is to power down and remove the batteries!!!
It is NOT necessarily a hung processor, BUT WHAT IS KNOWN AS "CROWBAR" IN POWER SUPPLIES!!!
The ONLY way to remove the crowbar condition of the regulator is to remove ALL power (AC and batteries).
Some people that try this great idea for a reset mod MAY not have the crowbar shutdown happen as the unloaded power supply voltage is MARGINALLY near the crowbar threshold of the regulator.
When I tried it (remove input or output), the regulator did not always shutdown.
I took some measurements and the unloaded and loaded unregulated voltages I found were VERY close to the maximum limits on the regulator so I am going to try and find another LDOV regulator that has a higher input voltage limit, or change the zener on the input to a 12 or 15 volt and place a small load resistor on the input to keep the regulator to keep the zener loaded when the real load is disconnected. Problem with that is the batteries will also be artificially loaded when no AC is being supplied... hhmmmmm.
Right now, I am actually shorting the regulator's output. I know,,, I know.... not a good idea, BUT the regulator DOES have short circuit protection, over power disapation shutdown, AND during the short, the current is only 70 mA and the regulator is rated at 100 mA max., so it doesn't really harm the regulator
STILL is NOT a good idea, but in the mean time.....
Looks like a better LDOV regulator is the best answer.... WITH the OP's great idea as well!!!!