On 5 Mar 2004 11:57:16 -0800, (Paul Probus)
wrote:

I have printed off the pdf version of the treadmill motor controller
schematic at the dropbox retired files. As I was looking it over, I
saw that there are some components that aren't labeled as to what
values they should be. For example, R2 and R4 are not labeled what
their resistance values should be. In addition, and I will admit that
I am a complete novice to electronics, I have no idea what L1 is
supposed to represent and there are no values for its size, so I
cannot even make a guess. I am hoping that those who developed the
schematic are still here.

While I do have interest in using the controller as-is (if I can get
the values needed) I am also interested in what it would take to
modify the controller for use to control universal motors because I
have need for controlling the speed of a large router, since the
TDA1085C controller IC was designed primarily for universal motors
according to Motorola's literature that I printed off.


L1 is probably just a hash filter, value not critical.

Check the application example schematic on the TDA1085 datasheet.
It's somewhat simpler than the treadmill motor controller and
presumably works. No L1 at all in that schematic, no transistors
either. The datasheet from ON Semi even has a PC board layout.
You'd probably need to change some values to work with a treadmill
motor, because the datasheet design is for a 0 to 15K RPM motor used
in a washing machine. .

There's another chip, the TDA1185A, that is designed for control of
universal motors with no tacho feedback, but I think it's no longer in
production. You might find some still floating around with some
diligent netsurfing. I have a few of them in my goodiebox I'm
saving for sewing machine speed controls (Singer Featherweight and
Singer 401) when I get around to it. One is reserved with Fitch's
name on it for his Singer Featherweight when he gets around to it.
Nothing Is Urgent.

You can buy a 15-amp router speed control for about $25 from Rockler.
It's probably not as good as something based on a TDA1185, but it
works better than I expected it would. It claims to employ some
voltage feedback speed sensing. I sure don't see it in the extremely
simple circuit, but Jeff Wisnia recalled a similar circuit and
reference to voltage feedback in the old GE SCR Manual circa late
'60's or early '70's. I found the circuit in my old SCR manual and
that indeed is what they're doing. It's not nearly as "stiff" as a
control would be with tacho feedback or current sensing as the
TDA1185 employed, but it's suprisingly good for such a simple circuit.

The best speed control would be achieved if you could devise a way to
add a tacho speedsensor to your router.