Collection of noobish questions for project

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I am trying to incrementally develop a control system and have a few questions for more experienced types:

  • Is there any reason not to use an Arduino Mega in a light industrial or domestic application? Assuming memory and CPU are sufficient. Does it have weak/failure points?
  • Do Arduinos have circuit breakers /resettable fuse built in? Or is it a good idea to put one into the 12VDC line?
  • Is there a straightforward way to integrate a battery that trickle charges and only comes on if the 12V supply fails; and have the failure detectable by the arduino (to alarm and avoid operating relays)?
  • I need to control a number of devices at various DC and AC voltages. I want to use something modular, with a reasonably high mean time between failure but good value and no more than 100USD ea - probably a bunch of SSRs that can easily be mounted in a cabinet of some sort. Is a DIN-based option best? Is there any sort of option like automotive relays with pluggable modules?
  • I want to be able to put the Arduino and a few interface bits - LCD, buttons etc - in a box and use a connector(s) with 50-55 pins to connect to external devices, ethernet etc. I was thinking about using a DB50 or a couple of DB25 and DB9 connectors. Are there any cost effective industrial alternatives? All the ones I have found (like Weidmuller HDD/HEE) are really expensive. Will the pins on a DB connector carry a decent load - e.g. 1 Amp?
  • if I'm going to have a number of devices that I want to mount in a cabinet, with the arduino enclosure sliding on rails against a backplane and mating with a connector(s). Is there a good option/standard to use, like a sub-chassis that goes into a 19" RU-based cabinet? I have other equipment that I'd like to mount together, and have relays, circuit breakers, etc in the same housing.

Thanks in advance....
Lee

2

A lot of questions here.

Is there any reason not to use an Arduino Mega

No

Do Arduinos have circuit breakers /resettable fuse built in? Or is it a good idea to put one into the 12VDC line?

No and No. They are a waste of time in a control application like this because they don't trip fast enough to protect anything.

battery that trickle charges and only comes on if the 12V supply fails

You need a diode to stop the battery discharging into the failed power supply.

probably a bunch of SSRs

Yes sounds like a good option, I would also budget for some mains filters to stop switch on interference crashing your arduino.

the rest is a matter of personal choice.

3

Thanks Richard - great post. I'm digging through the Opto 22 site now. Just the sort of thing I was after...

4

Is there any reason not to use an Arduino Mega in a light industrial or domestic application? Assuming memory and CPU are sufficient. Does it have weak/failure points?

I've found some code (like NewSoftSerial) doesn't yet work with the Mega. Make sure any libraries/sample code/shields you're planning to use are compatible. For another example, the I2C/TWI pins on the Mega are in a different place than the Duemilanove.

Do Arduinos have circuit breakers /resettable fuse built in? Or is it a good idea to put one into the 12VDC line?

No and yes :slight_smile: They may not protect your circuitry but a fuse will prevent a fire in the worst case.

Is there a straightforward way to integrate a battery that trickle charges and only comes on if the 12V supply fails; and have the failure detectable by the arduino (to alarm and avoid operating relays)?

Here's a circuit to provide some backup power on the +5V line. I suppose you could adapt this to 12V but it's probably not necessary. A simple voltage divider can be connected to 12V and an A/D input to sense when voltage is lost.

Not much to say on your other questions. Whenever you're talking about industrial solutions, it's going to be expensive :frowning:

--
The Quick Shield: breakout all 28 pins to quick-connect terminals

5

Do the opto G4 modules just screw into place? Do the pins just mate with the holes on the board- no solder? It looks lile it, but there don't seem to be proper sockets...

6

I'm sold on the Opto stuff. The modular relays with manual switches are perfect. With the boards/racks, the various options are difficult to distinguish between - if I want to use a header, what's the difference between 'isolated control', 'common TB' (sounds painful) and other the other 16 channel options?

One other thing... If using a Mega, given that there's no 'pro' version, what's the best type of connector to mate with the Mega header sockets? IDC? I'd like to be able to easily swap the arduino out, and also have a fairly secure connector; and polarised. There don't seem to be options that easily match/mate with the various arduino headers. Maybe I need to search harder?

7

Thanks - the cost is OK for me. I will try to find alternatives, but this will be a commercial application so am not too fussed. These are the type of relay I want to use - happy to pay a premium for the switches

for AC - http://www.opto22.com/site/pr_details.aspx?cid=4&item=G4OAC5AMA

for DC - http://www.opto22.com/site/pr_details.aspx?cid=4&item=G4ODC5MA

8

Watch out for the voltage drop across those DC output modules: it's trivial when you're switching 120VAC, but I had to go with a mechanical relay on one project because the 12V equipment wouldn't tolerate the reduced power supply.