Model Rocket Continuity Check on Arduino I/O Pin ..#2

Thread Starter

LydaRA

Joined May 6, 2021
37
Hey moderator: Thanks for the effort. But by separating it from the original post, how are the OP and responders I was trying to speak to to get notified? And since there doesn't appear to be a PM tool here, how do I direct the question to the particular poster--the one with the drawing I would like to review?
 

ericgibbs

Joined Jan 29, 2010
12,932
hi L,
Note: the last time the original post was on AAC is Last seen Jul 7, 2014
Do you really want to wait for him .? :)

Post what you have here and your query and we will do our best to help you.
E
 

Yaakov

Joined Jan 27, 2019
3,161
Hey moderator: Thanks for the effort. But by separating it from the original post, how are the OP and responders I was trying to speak to to get notified? And since there doesn't appear to be a PM tool here, how do I direct the question to the particular poster--the one with the drawing I would like to review?
The person who posted that thread was last seen in July of 2014. If they are still receiving email notifications, they will get one about the thread getting a new post. It is very unlikely they will know about it, though.

If you are going to get help, it's going to be from the people here now, and adding posts which may well only be tangentially related to the original thread is not helpful for people in the future.

There are "conversations" here, which you will have access to after 10 posts. You can start one by viewing the person's profile.
 

du00000001

Joined Nov 10, 2020
63
Wow, "great minds think alike." I'm about to build a 16 rocket semi-simultaneous launch controller for the Cub Scouts. And I'm figuring out the igniter continuity circuits now... Any chance to see diagrams & photos of what you ended up with? Thanks in advance.

Mod: link to old Thread
https://forum.allaboutcircuits.com/threads/model-rocket-continuity-check-on-arduino-i-o-pin.96429/
Let me cut it short (I didn't participate in the '2014 discussion):
  • A simple resistive divider (to provide for voltage adaptation) parallel to the outgoing contact of the then start button would have done. Maybe connected to an analog input - depending on the igniter's I/V curve.
    (If you press the button and nothing changes, continuity is obviously not given.)
  • Another thing would be to check continuity prior ignition: in this case I'd suggest to use an AC or pulse train signal with an amplitude low enough as not to ignite.
    On the transmitting end this is easily done by resistive dividers - plus a series resistor to sense voltage drop in case of continuity.
    On the receiving end this might require some amplifier(s), but quite simples ones: uncritical OpAmp circuit - polarity d/c.

Enough information to follow the lead ?
 

JustSomeHuman

Joined Oct 2, 2016
15
An Arduino Due has 12 Analog inputs and a slug of I/O pins. If you use a resistive divider on one of the I/O pins configured as an output to limit the voltage and then use one of the Analog inputs to sense the voltage drop across a resistor in series with the igniter to determine continuity. 5BC17CF4-013D-4DD5-9E26-CEEDBB984C90.jpeg
 

Thread Starter

LydaRA

Joined May 6, 2021
37
Hmmm. I've been planning around the Arduino Mega. Thought the Due was discontinued. However those CAN pins look intriguing... Has anyone enabled those? Is there a compatible API?

My setup will require three Arduinos (RSO Box + 2 Pad Boxes). They'll be spread out too far for I2C: RSO Box <-- 15'-100' --> Pad Box #1 <-- 15'-35' --> Pad Box #2
 

JustSomeHuman

Joined Oct 2, 2016
15
Hmmm. I've been planning around the Arduino Mega. Thought the Due was discontinued. However those CAN pins look intriguing... Has anyone enabled those? Is there a compatible API?

My setup will require three Arduinos (RSO Box + 2 Pad Boxes). They'll be spread out too far for I2C: RSO Box <-- 15'-100' --> Pad Box #1 <-- 15'-35' --> Pad Box #2
I just checked the Official Arduino Store. It looks like the original Due was discontinued, having been 73455CCE-13DD-4495-A4F4-40F64A6154CA.jpegreplaced with this new one.
You use the Arduino IDE to program the Arduino Boards. The Arduino IDE is free, easy to learn and use. It is available for Macs, Linux machines and Windows. There are more involved ways to program their boards, but these techniques are only necessary for very specialized situations.
 

JustSomeHuman

Joined Oct 2, 2016
15
Hmmm. I've been planning around the Arduino Mega. Thought the Due was discontinued. However those CAN pins look intriguing... Has anyone enabled those? Is there a compatible API?

My setup will require three Arduinos (RSO Box + 2 Pad Boxes). They'll be spread out too far for I2C: RSO Box <-- 15'-100' --> Pad Box #1 <-- 15'-35' --> Pad Box #2
Oh and BTW, the new Due version has ADC and DAC ports. This would make your project almost trivial. And as well as you noticed a CAN bus interface.
 
Unfortunately, it looks like just two such ports on the boards. I need eight channels.
Well, two things. First you must not understand how a CAN Bus works. The first operational term is the word BUS. CAN is an acronym for Control Area Network, again the operative term is NETWORK. CAN Busses are used in virtually all modern cars. Most all of the sensors and devices in the modern cars run on ONE CAN Bus.

Second, I don’t understand why you are so enamored with using a CAN Bus. Yes it would solve your problem, but it would require eight different CAN Bus compatible boards. You can obtain any one of quite a few micro controllers with CAN Bus interfaces from Adafruit or certainly from other sources. Now you are into programming the front end of the bus, possibly a Arduino Due, and probably similar code in each of the eight “nodes” on your bus. But you still have the problem of how to sense continuity from each of the boards on the bus.

Using the eight analog to digital converter inputs and one of digital to analog outputs, your hardware is essentially complete.

I hope this helps
 

Thread Starter

LydaRA

Joined May 6, 2021
37
Well, two things. First you must not understand how a CAN Bus works.
Sorry, mixing two different aspects of the project:
1) CAN Bus or RS485 Modbus would be for command bus between three connected Arduinos. The RSO Box is a "master" and two "slave" Pad Boxes each host eight rockets.
2) Each Pad Box needs to use eight relays to the eight rocket igniters. With the igniters on C, continuity/ready status is to be checked on NC, and 12V 2A pushed through to launch on NO.
 
Sorry, mixing two different aspects of the project:
1) CAN Bus or RS485 Modbus would be for command bus between three connected Arduinos. The RSO Box is a "master" and two "slave" Pad Boxes each host eight rockets.
2) Each Pad Box needs to use eight relays to the eight rocket igniters. With the igniters on C, continuity/ready status is to be checked on NC, and 12V 2A pushed through to launch on NO.
OK, that makes things a more clear. Yes, you could certainly use one CAN Bus for the master to “talk” to the slaves. I got confused when you mentioned that the Due only had one CAN Bus and you needed eight CAN Buses.
So three Dues tied together on one CAN Bus with the eight Analog to Digital on each Due checking the continuity on its eight igniters. When all three Dues are happy about all the igniters, then the master could issue a launch command. Each Due could use one Digital I/O pin to close one relay to launch its eight rockets. Or if you wished, you could use eight I/O pins to close eight relays, or perhaps only closing only the relays that will fire only the rockets that have continuity tested OK.
 

Thread Starter

LydaRA

Joined May 6, 2021
37
Each Pad Box needs to measure three states of each of the eight rocket igniters' resistance:
1) Open (no rocket, >2 Ohm);
2) Ready (expected to launch, 1 Ohm);
3) Short (igniter bent/leads touching, < .75 Ohm).

Unless I find such an eight channel measurement circuit... I assume need to build something that sources from an Arduino digital output pin (so can just check whichever channels desired), run through the igniter, then ultimately brought back into an Arduino analog input pin.

But then need to separate this 5V <50mA (igniter safe test) measurement from the launch side of 12V 2A! I assume this separation is via a relay, definitely double-throw (to get the NC & NO). Maybe a double-pole...or just tie the 5V and 12V grounds together?

Oh for something time-tested for multi-circuit measurements, or at least better circuit diagram than I've got...
 
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