Experimental Physics and
Industrial Control System

Ryan Pierce <[email protected]> · Mon, 7 Mar 2016 22:25:34 -0600

I'm wondering how best to model the following situation....

I have a number of DS18B20 temperature sensors on a OneWire serial bus

controlled by an Arduino Mega. A Raspberry Pi runs an IOC and

communicates with the Arduino via asyn. In other words, I'm implementing

a smaller version of the solution I suggested back in January to measure

a large number of temperatures.

Each of these sensors has the equivalent of a unique MAC address that is

8 bytes long, and the sensors can be hot swapped on the bus. I'd like an

operator to be able to retrieve these. I can easily have the Arduino

scan the bus and create a list of addresses. I'm just not sure how to

get that info back to the IOC.

I know I can create individual stringin records for the 1st, 2nd, 3rd.

etc. address that was scanned, up to a defined maximum limit of

temperature sensors, and have the Arduino return these as hex formatted

strings. But I'm wondering if there's a better way.

Ideally, I'd like it to be returned as an array of type stringin. But I

don't know if such a thing exists in EPICS, or if it does, how to pass

it through asyn.

I can't return it as a single space or comma delineated string either,

since I exceed the 40 character limit with 3 devices.

I considered trying to pass these in binary form and convert it as hex

for operator display, but I don't know if a 64 bit datatype exists.

Is this something that a waveform record could do? If so, could CSS Boy

display this as some kind of box or list of strings?

Thanks,
Ryan

P.S. Latest EPICS controlled beer brewing update: As I mentioned last

September, I had been stalled waiting for a CNC mill at a hackerspace to

be repaired so that I could easily do precision drilling for the 60+

holes I need to mount jacks on a control box. The mill still doesn't

work, but I found a better solution: a friend with a waterjet cutter. It

made short work of cutting all those holes, as well as a panel insert

for more DIN rails. So things are progressing.... Update here:

http://www.mackenziegems.com/2016/02/21/cnc-beer-part-3-fusion-360-and-waterjet-overkill/