Control Panel Project

(under construction)

This was the first control panel I ever built.  Originally, it was capable of handling only 10 circuits. All the wires from the (10) devices had to be brought to the speaker connectors at the top of my panel.  The first 10 connectors matched up with the LED and push button switch at the bottom of the panel. The last two connectors were connected to ground.  Later I added a multi-position switch which gave it the capability of handling 50 circuits.  

How it Worked

This panel is designed to function safely on DC voltage up to 48 volts.  Because of the LEDs (light-emitting diodes), if I were to use more than 48 volts, I would risk having too much current flowing through the LEDs which could (and probably would) pop the igniters, resulting in a short (but intense!) fireworks display.  Only a small amount of current (Amps) is needed to cause the LEDs to emit light.  A current limiting resistor is placed in series with each LED (refer to schematic diagram further down this page).  When one of the fire switches are pushed, the full amount of current flows through the switch to the e-match causing it to ignite.  

 I use four 6-volt lantern batteries connected in series, with alligator clips, as my power supply.  The batteries are connected to the positive and negative terminals of my panel.  Since this panel uses LEDs as indicators of continuity, the positive from the battery must be connected to the positive terminal on the panel (in this case the red battery terminal post), and the negative from the battery to the negative terminal post on the panel (the black terminal post).  

The control panel also has an on/off switch.  For safety reasons, the switch should be in the off position before any circuits or batteries are connected.  The battery array should be the last thing connected, after all the device circuits are connected. 

Like I said earlier, I used speaker terminals as my connectors for the varies circuits.  The first 10 speaker terminals match up with the 10 (normally open, momentary contact) push button switches.  The last two speaker terminals are connected to ground (the negative terminal).  To make a complete circuit to switch number one, a pair of wires is connected to an igniter, or series of igniters, out in the field.  One of the two wires is connected to the first speaker connector and the other to one of the last two speaker connectors (the ground connectors).  At this point, if the batteries were connected and the on/off switch were in the "on" position, the LED would be lit, indicating a completed circuit.  The remaining nine circuits would be wired in the same manner.  Of course the 2nd circuit would be connected to the second speaker terminal and so on.  The wires going to the ground terminals may have to be twisted together into two groups and each group inserted into one of the two ground terminals.

After all the device circuits are connected and the batteries are connected the switch can be placed in the on position.  At this point, the 10 LEDs should light indicating all circuits are working and the fireworks show is ready to fire!!

Building the Control Panel

Yes, I meant to put the "how it worked" section before the "building" section. 

Step 1   

You will need to acquire the parts for the project.  I purchased may parts from Hosfelt Electronics

and RP Electronics .  

Parts needed:

1 - project board -  I used a piece of Plexiglas (spray) painted  black.

3 -    Four push type terminals for speaker        317-204 : 4 Push Type Terminals mounted on flat plastic plate

10 - normally open momentary contact switches

10 - Light emitting diodes (LED) (3 mm or 5 mm)

10 - 4.7 k ohms resistors  (1/4 watt are fine)   CF-1/4-4.7K : 4.7K OHM 1/4W PKG 100

1 - on/off (stsp)  toggle switch 453-320 : SPST 3A, On-Off, Solder

2 - binding (battery connecting posts) posts (one red, one black)     

Step 2

Drill/cut the holes you will need in your project board.

Then mount the hardware.

Now you are ready to begin wiring/soldiering together all the components.  Here is a simple schematic diagram that shows only the first three circuits.  The last seven are wire the same as the first three. You will need. Wire, soldier, and a soldiering iron.

 

This is what mine looked like after I was through.  (Looks like a mess)

 

Resistor selection

The selection of the proper resistors for this project is extremely important.  If the value of the resistor is to low, and the voltage to high enough current could be sent through the resistors and LEDs to fire the electric matches (e-match).  The current needed to fire most commercially manufactured e-match is 0.5 -1.0 Amps or 500 to 1000 milliamps.   So the value of the resistors must be high enough, at max voltage (48 Volts), to keep the current flowing through the resistors and LEDs well below 0.5 Amps. (No fire current is typically around 0.15 Amps or 150 milliampes).  Any current close to 0.5 Amps could still fire the e-match.  To over come this we want to design the circuit to allow enough current to flow to just cause the LED to light.  The current required to cause an LED to emit light is 0.006 Amps or 6 milliamps.  Well below the current needed to fire an e-match.   To calculate this we use Ohms Law:  E (voltage) = I (current in Amps) x R (resistance in ohms).  As stated earlier I designed my system to use a maximum of 48 voltage (DC).   I decided to limit the current through the LED to 10 milliamps (0.01 Amp).  Using these figures lets see what the value of my resistors should be:   48V/.01A = 4800 ohms or 4.8 ohms (I actually used 4.7 k ohms resistors).

48 Volts DC is the MAXIMUM voltage  I use with this control panel.  Typically, since my wire runs are not extremely long I use 24 Volts DC.  

This is the amount of current flowing through the LED at 24 V.

24V/4700ohms = 0.005 Amps or 5 milliamps (I've fired with 12 V before with gives me 2 milliamps through the LEDs.  They still emit light, its just not as bright). 

IMPORTANT NOTE:  Unlike resistors (and e-match), LEDs will only pass current in one direction.  Current flows in the direction the arrowhead (symbol) is pointed.  I tested my LEDs with a 9 V battery.  When they lit up, that was the direction of current flow.