Rotary Encoder help

[victorf]

I have a legacy product that I am seriously considering for upgrade. The product contains two rotary encoders supplied by US Digital. They are interfaced to a pair of HCTL-1000 general purpose motion control ICs made by HP (now Agilent). I understand that these ICs are obsolete.

The encoders are easily read by a micro-controller. The encoders are 4096 counts per revolution units and are being used to give me the elevation and azimuth angles of a theodolite. Since the theodolite is manually operated there has never been an issue of the angular data keeping up with the user operation. The HCTL-1000 is clocked with a 1MHz crystal.

Agilent makes a more sophisticated version of the -1000 known as the HCTL-1100. At a price of $42 per for small quantities it is getting too rich for my blood. If I were to produce more product I would need 2 encoders at ~$60 per and 2 -1100s and this will place my product well beyond a reasonable price point.

Has anyone a less costly solution? I need to periodically (once every 15, 30 or 60 seconds) read both encoder current count and compute some stuff and wait out the remaining time and do it all again. Reading the -1000 was a no-brainer. I just read the high byte clocked into the output
register, ask for the low byte and read that and then combine them into a count and convert the count to an angle.

Any enlightenment will be appreciated.

Vic

[GTBecker]

What processor, Vic?

If the processor is fast enough it can count quadrature edges on two axes (with a little external logic) via interrupts and still have lots of time to massage the data.

I have such a device that started with a BX-24. At the time each axis resolution was 1.25 degrees; the BX-24 could keep up at full motor speed. I increased the axis resolution to 0.25 degree and immediately found that a BX-24 could not keep up with the resulting interrupt rate. It now runs a ZX-24n - which is fast enough to handle my fastest axis motor drive rate at the higher resolution.

In your case, you'd need to count accurately at the highest slew rate of your instrument, I imagine.