06-04-2019, 10:12 AM
I decided to try and make up a TouchDRO setup on the cheap. An MSP430 Launchpad was $20 and the Bluetooth module $7 (Australian dollars, so about US$19 all up). Those bits, and the quadrature firmware went together no problem at all. For the scales, I decided to get this read head:
https://www.machineryhouse.com.au/D696
and this magnetic strip:
https://www.machineryhouse.com.au/D694
Which all seemed pretty cheap for a magnetic scale, and, potentially, easy to install.
First hurdle was the read head had no pinout or colour code, nor supply voltage spec, so I had to hunt around, but found the wire colour code matched similar-looking devices. Then, with a 5V supply to the head, the output signal had a 75mV amplitude, not the TTL signal I was expecting. I wasn't sure if it was due to the supply voltage - raising it to 7V increased the signal to 100mV, but I wasn't willing to go above that for fear of frying the read head.
My theory is that these heads, being comparatively cheap at US$62, might be a custom design for the "Optimum" brand DRO unit, and maybe they skipped some signal conditioning circuitry in the head. Or maybe I'm way below the required supply voltage, I dunno.
So I put the complementary signals from each channel through an instrumentation amplifier to bring the signal up to a single-ended 0-3.3V output. That interfaced just fine with the MSP430, and the TouchDRO display increments and decrements accurately and repeatably.
However, the resolution is only 0.5mm, which seems to be 1/100th of what I was expecting for a 5µm system.
Any suggestions on what to try next?
https://www.machineryhouse.com.au/D696
and this magnetic strip:
https://www.machineryhouse.com.au/D694
Which all seemed pretty cheap for a magnetic scale, and, potentially, easy to install.
First hurdle was the read head had no pinout or colour code, nor supply voltage spec, so I had to hunt around, but found the wire colour code matched similar-looking devices. Then, with a 5V supply to the head, the output signal had a 75mV amplitude, not the TTL signal I was expecting. I wasn't sure if it was due to the supply voltage - raising it to 7V increased the signal to 100mV, but I wasn't willing to go above that for fear of frying the read head.
My theory is that these heads, being comparatively cheap at US$62, might be a custom design for the "Optimum" brand DRO unit, and maybe they skipped some signal conditioning circuitry in the head. Or maybe I'm way below the required supply voltage, I dunno.
So I put the complementary signals from each channel through an instrumentation amplifier to bring the signal up to a single-ended 0-3.3V output. That interfaced just fine with the MSP430, and the TouchDRO display increments and decrements accurately and repeatably.
However, the resolution is only 0.5mm, which seems to be 1/100th of what I was expecting for a 5µm system.
Any suggestions on what to try next?