IBM PCjr

A couple of things. Firstly I had to explain that if you connect cells/batteries in series then the voltages add but if you connect (equal voltage) them in parallel the voltage is unchanged but the internal resistance and capacity are increased. Secondly I had to explain that as the battery could 'float' with respect to the 0V rail, you could use a -5V regulator as a supply for a board of logic devices. The point is that you can connect the -ve lead of your voltmeter wherever you like. There is no god-given 0V point. If you have a circuit that takes in 3V and gives out -5V (a common SMPS chip can be configured to do just that) you can easily run some TTL from it. The '-5V' line from the PSU becomes the '0V' line on the logic and the '0V' line on the PSU is the '+5V' line on the logic. Of course you have to be _very_ careful if any voltages are referenced to anything else, like mains ground. I have a 5V 50A _linear_ in one of my Unibus expanison boxes (a 3rd party one - DEC almost always used SMPS's). It runs hot. -- -tony ard12(a)eng.cam.ac.uk The gates in my computer are AND,OR and NOT, not Bill