Ardunio

[knighty]

anyone use an ardunio much ?

the controller on my new (2nd hand) machine at work is dead

...and a new one will run into 4 figures... and it wasn't very easy to use anyway (it was a total pita)


so I'm thinking I could build an Arduino system instead

it's a drying machine for dog treats...

sensors/outputs are pretty easy

need to sense, air temperature going into the machine, inside the machine, and exiting the machine
and the humidity going in, inside, and coming out
start + stop buttons

outgoing controls are....
heaters (probably 2 outputs here for full/half heat)
inside fan
exhaust fan (this is currently inverter controlled, could still use the inverter?)
refrigeration compressor

simple screen output, to show what's going on....
time it's been running, the 3 temperatures, and also maybe something to show you which relays are powered up

everything inside the machine is already powered up via low voltage relays, so that's not a problem
(tho might still need something to power these between them and the arduino)

anyone know how easy/reliable this would be to do before I buy the gear ?
I did programming at A level and for my degree so I'm happy with that

I was thinking of using these as sensors...
http://proto-pic.co.uk/hih-4030-humidity-sensor-breakout/

anyone know if they'll be ok up to high temp ?  I shouldn't need to go past 100'C but it would be better to built something to take 200'C just incase...

these temp sensors look good too... nice high temps, but no humidity :-(
http://proto-pic.co.uk/thermocouple-type-k-glass-braid-insulated/

can I use another off the shelf humidity sensor instead ? (one better matched to the high temps)

[Baz]

There has been a lot of interest in it but not much posted for a year. Go back about a year or so in this section and you will find several threads. Or try a serach on Ken Boak if I have remembered his name correctly. I haven't tourched mine for ages and must restart from scratch. There are some boards around that provide all the interfaces you mentioned. All the links are on my old computer so can't point you there just now. Proto-Pic looks like a new name in the game but much will have changed in the year I have ignored it.

[Baz]

http://www.nuelectronics.com/
found it. These are the people I got most of my boards from.
For temp sensor you might try the ones used in solar water systems as they go above 100C.

[Fintray]

Knighty
I think a PLC using ladder type logic would be simpler to programme and interface to the existing sensors and relays.

[ericw]

I wouldn't use thermocouples, it requires quite complex circuitry to measure the small voltages they generate.
1 wire DS18B20's will go to 100 degrees, above that I would suggest a thermistor.  If its just a fixed temperature you need to control then its easy, if you want to measure over a range then you would have to do some calculations to compensate for the non linear resistance v temp characterstics.

You certainly will need something to buffer the Arduino outputs to the relays, output shields are available or you could use something like a ULN2003

[StBarnabas]

If you can program in "C" the Arduino should be fine. You can get relay shields easily and a DHT11 (about £4) will do temperature and relative Humidity. Look at http://www.nuelectronics.com/estore/ as Baz recommends. I would recommend the DS18B20 as a temperature sensor. This is very easily interfaced with the Arduino. It is worth also looking at EricW posts and obviously KenB as mentioned earlier -

Fintray
I agree that PLCs are easier to program, I'm not sure there is much in it regarding interfacing. However unless PLCs have come down in price recently they are considerably more expensive than the Arduino.

If you are skilled in programming PICs then the 16F1827 has easily enough capacity to do what you need. This is around the £1 mark so easily the cheapest option.

the DS18B20 only go upto 128 Degrees C so as Eric says thermistors would be a better option if you want to go to 200 degrees. One of the HalfBee codes for the PIC12F683 has two thermistor inputs and uses a lookup table to convert to temperature.

[knighty]

thanks for all the replies, you guys really know what you're talking about !

I feel much more confident now :-)

my little brother is an engeneer and has done quite a bit of PIC programing as part of his job so that would be an option....

but I think I'd rather go with something I could work with myself... at first I'll have to experiment with the machine settings to get it runing perfectly for what I want.... what kind of tempriture to run at, how fast to warm up, and when to stop (after x time at y'C or when the exit air humidity gets low enough...

I'll order an Arduino tonight with the sensors I'll need and have a play with it at home before I touch the new machine

I've also been thinking I could add an ethernet add-on thing to it so I can monitor the maqhcine from a PC and learn a bit more about how it runs, grapys of tempriture/humidity etc...

the more I know/learn about it, the more efficiently I can run it.... the manufacturers set up profiles in the built in PLC for you, but they're very basic and just what the #tech guy' they send out guesses will be right for you....

there should be a sweet point between running for a short time at a high temp and a long time at a lower temp where I'll use the least power
(my electric meters were a blur when it ran for 5 min the other day)

I'll post back when I get home and have had a better look around and bought some bits :-)

p.s. I did C for my degree so should be able to pick it up again pretty quick :-)

[knighty]

a check reply before I buy the bits needed...

(nuelectronics were sold out of a lot of the things I need, so had to look elsewhere)

Arduino board - http://proto-pic.co.uk/arduino-mega2560-rev-3/
lan shield - http://proto-pic.co.uk/arduino-ethernet-shield-rev3-without-poe-module/

temp sensors - http://proto-pic.co.uk/thermocouple-type-k-glass-braid-insulated/
humidity sensors - http://proto-pic.co.uk/hih-4030-humidity-sensor-breakout/

relay board - ebay link


had a think and I won't bother with the screen if I can display everything via a web server via the ethernet shield - means I can see what's going on, and change settings more easily while I fine-tune the machine

relay board might be a bit lazy, but it's more professional than anything I could make, it won't be switching much power because everything is already powered via relays/contactors etc... also has a lot more outputs than I'll need, but I'd rather have too many than too few !


anyone see any problems ?   I don;t think the humidity sensor will take the heat inside the room, but it will do while I have a play with it :-)

[johnrae]

£17 for a 16-channel relay board  What a bargain !

[Baz]

bargain indeed. Looks like they might be optos in front of the drivers hence the 15-25mA drive current. That might be a problem not sure about capacity of arduino driving lots of them.
Also look carefully at the drive pins used on each shield. They tend to get designed as if only one is used at a time so all want to use the same lines.

[knighty]

slight change of plan, dropped the separate temp and humidity probes and bought 3 of these instead...
http://proto-pic.co.uk/humidity-and-temperature-sensor-dht22/

combines them into one, and saves about fifty quid at the same time :-)

[Countrypaul]

Looking at the relay shield it doesn't appear (to me anyway) to have one input for each relay. It only appears to have input pins 1,3,5,7,9,11,13, &15 - in which case is the input binary then why so many pins?

If each relay is not separately addressable are they latching, or how do you keep one switched on whilst switching another?

I know I must be missing something, but can't see what!

I have bought a single relay to play with, but am looking at something with many more on, and the one highlighted seems to be available from several suppliers, but none explain how to address each relay.

Paul

[knighty]

if you zoom in a bit, the even numbered pins are on the other side of the connector... it goes


!2!4!6!8!10
!1!3!4!7!9

etc.. :-)

[Countrypaul]

Thanks knighty, I never thought about a second row  - seems so obvious now 

Paul