Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

hello all

A few questions on fuser feed rate and temperature sensing.

I have pullrd apart an old HPLaserjet5L and have the fuser attached
to the stripped down chassis.

I recovered the stepper driver chip from the pc board and am
currently successfully driving it with a PIC micro. The rollers will
accept a 1.6mm (1/16 inch) board with a gentle push to engage it in
the rollers. What feed rate have others used?

A general stepper question - Should steppers be driven with a short
pulse then allowed to free-wheel. It seems that this might make the
motor turn more smoothly. How would I work out how long the pulse
should be?

I have heard that the temperature sensor is a thermister. Can
thermisters withstand this temperature without damage? I intend to
control the temperatue via an analogue input on the PIC. My sensor
measures 500 k ohms at room temperature, which is too high to use as
one leg of a voltage divider to dive the analog input (10k max
source resistance). What sort of resistance would I expect at fuser
temperature? I know I can buffer the voltage divider with an op-amp,
but would rather not.

To get the right temperature I was going to use a trial and error
method - estimate a value to switch at (intentionally too low to
start with) and increase it until it works. My digital multi-meter
does not have a temperature function.

thanks

pete