Re: Update on closed-loop to the computer with Gecko 320

Jon,

1) Do not use the HCPL-2530. It's gain is only 9%.

2) Do not use a 74HC part as a buffer. It's only good for +4/-8mA.
Use 74AC parts; they are good for +/-24mA. Same pinouts (7414 =
74HC14 = 74AC14).

3) Meant as written. ENC+ (+5VDC) is also the virtual analog ground.
This makes it a node, meaning current flows into and out of it. If
current flows into it (from internal analog circuits), it causes the
node voltage to rise above the regulated +5VDC. A 470 ohm resistor
ensures that can't happen; the encoder load normally takes care of
that.

4) It is symmetrical. Your brushes may have set in a direction. Run
the motor a few hours in the opposite direction and try again.

5) PID tracking is an unecessary luxury for this price drive. The
drive is tuned for a particular system power supply that normally
will not change over the service life of the system. That leaves
ripple voltage which is an insignificant second-order effect.

6) Fine-pitch placement requires machine vision. This slows a machine
down from 15,000 parts / hr to about 3,000 / hr. and we have a
Zevatech FS740 for that. I try to avoid fine-pitch packages for that
reason; time is money.

Whose FPGAs are you using? Xilinx? I ask because I'm learning to use
their 9500 series CPDLs which I will eventually use to replace the
SOIC glue logic in all our drives.

7) Eliminate the D term by turning the DAMP trimpot full CCW.
Eliminating the I term requires shorting an 0805 capacitor.

Mariss