Go Down

Topic: Method of measuring ressistance with arduino. (Read 1 time)previous topic - next topic

ThomasH

Oct 27, 2011, 07:36 am
I have a project in the works where measuring resistance would be of use.
Basically what I'm trying to do is create a fireworks launching platform, using electronic fuses.
These fuses ignite at 12v and will have a pretty high resistance.

What I need is to create a circuit to detect whether the output is connected to a fuse or not.
the measurement doesn't have to be accurate. But must be able to differentiate between a empty output and a live output.
I will try to get my hands on one of the fuses soon, so I can find out exactly the resistance over the fuse. And maybe figure out the current need to fire the fuse.

Is there a very simple way to tell if the fuse is in place or not? If not; what is the complex way of doing it?

-Thomas

#1
Oct 27, 2011, 08:56 am
Take a voltage reading across the two pins, look at the difference.
If reading 12V, will need resistor divider to get into 0-5V range.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

123Splat

#2
Oct 27, 2011, 07:03 pm
In continuity check firing systems, you apply a voltage, lower than what is required to fire the detonator, to check continuity.  If you can, selectively, connect the firing circuit branch high side to an Arduino Supply pin (+5, or +3.3, if you are using a 12v firing circuit); and the firing circuit branch to an Arduino Digital pin which has a 10K Ohm wired to ground (reads zero, low, when nothing else is connected), you shoule read a one, or high, to indicate coutinuity, or a zero, low, to indicate open circuit (no fuse connected, or fuse burned open).  You should be at safe voltage/current levels to avoid inadvertantly setting off the fuse.  The only problem with this setup is that you have to have a way to compleetly disconnect the Arduino (power and digital input) from the firing circuit, before firing (otherwise you WILL damage the arduino).

A safer and simpler way is to wire a conventional type firing circuit with a D.P.D.T. throw switch on each branch: one side of the switch connects to the low voltage test circuit (a low voltage source and an indicator, like a LED or a lamp); the other side of the switch connected to the Firing supply buss (+12V, in your case, buss connected/disconnected by another switch, which is the master arming sw); the common poles of the switch connected to the firing branch (the lines to the fuse).

Operating procedure:
1) disarm the system by opening the Master Arming Switch (good idea to disconnect your 12V source also).
2) wire in the firing Branches; place the fuse, connect fuse to branch, repeat for all other branches.
3) confirm circuit test switches are in center/neutral position.
4) connect branches to respective terminals on firing box.
5) connect test voltage to firing box.
6) circuit continuity test: throw each branch switch from neutral to test, confirm indicator on, return switch to neutral position.  Repeat for each branch.
7) decide firing mode;  all at once, or individually fired.
if firing mode is all at once: verify master arm is off/disconnect/dissarmed, throw all selected branch switches to fire position.
if firing mode is individually: verify master arm is off, verify all branches switched to neutral position.
Call firing warning and wait for all clear.
9) Verify firing supply is reconnected to firing box and master arm is off.
10) FIRE: if mode is all at once, switch master arm from off to fire/on/connected.
if mode is individually, switch master arm from off to fire, switch branch switches to fire position in desired order.
11) verify successfull detinations and follow post firing safety precautions switch all switches on firing box to off position, disconnect firing supply, disconnect all branch circuits and shunt branch lines (short them together).  call all safe and go check the damage.

ThomasH

#3
Oct 27, 2011, 10:46 pm
@123Splat

Would it be possible to have the analog signal trigger an input to a shift register? that would save alot on pinspace and still give me a good source of information. The plan is to use the arduino mini to save on space.    And there are not many pins to go around on those.

As for protecting the shift register i have an idea, I will be using 12v relays to fire the fuse. If i wire the continuity testcircuit through the NC terminal of the relay; That will disconnect the NC side way before the NO side is properly connected, and should protect the sensitive comportment's from the 12v.

One of the problems with this is that the NC and NO switches uses a common ground, so id have to wire the +5v into the same GND. But i believe i could use two diodes to separate the different voltages from each other. Does this sound doable to you?

And one other thing, they will always be in sequential firing mode, since its going to be a slave device, controlled by another Arduino.

-Thomas

Go Up