If you use LATCHING relays, and they have an extra pair of contacts, you can build a shift register/ring counter, with no external logic. I don't know WHY you'd want to avoid external logic, but you can.

Would using external logic be easier? What would be your recommendation?

 

After doing more research and thinking about this more, maybe it would be better to sense the input current that way the "test" current will not cause the circuit to advance. With that in mind, perhaps it would be best to use an ATTiny to control the circuit. I have a fair bit of programming experience and could program the ATTiny once the circuit is designed.

 

The controller sends the pulses based on how I program it to. So whatever would work best for the control circuit, I can program it to do. It always outputs for 2 seconds, but I can control how many of the pulses and the time in between them.

Not quite what I asked. The gadget you have asked about is a fixed device, not programmable. It will do one thing only, step through a fixed number of outputs based on an input waveform. What should it do when after it reaches output #12? This gets into its control and reset system. Once it is powered up, either from input pulse #1 or from an internal battery and an on/off switch, will it need to be able to make more than one pass through the 12 outputs, or is it 1 through 12 then done for the night? I get that it could get pulsed through 1 to 4, then sit for a while, then 5,6,7, then sit again, etc.

ak

 

Not quite what I asked. The gadget you have asked about is a fixed device, not programmable. It will do one thing only, step through a fixed number of outputs based on an input waveform. What should it do when after it reaches output #12? This gets into its control and reset system. Once it is powered up, either from input pulse #1 or from an internal battery and an on/off switch, will it need to be able to make more than one pass through the 12 outputs, or is it 1 through 12 then done for the night? I get that it could get pulsed through 1 to 4, then sit for a while, then 5,6,7, then sit again, etc.

ak

After it reaches output #12 it would be done. It would only need to make one pass through the outputs.

 

Would it be difficult to sense when the input current is above a certain threshold? That way the "continuity" current that is periodically sent out by the controller would not cause the circuit to advance to the next output.

 

Yes, I'm working on how to deal with that. It would help to know what the controller expects to see when it puts out the continuity pulse.

ak

 

Yes, I'm working on how to deal with that. It would help to know what the controller expects to see when it puts out the continuity pulse.

ak

I will try to get some measurements from the controller. Just for clarification, when I am talking about the controller, it is the device that sends the pulses.

 

Yes, that is the controller, and what we are working on we'll call the distributor.

ak

 

Here is a link to the controller:
http://www.cobrafiringsystems.com/index.php?route=product/product&product_id=51

I'm confused; unless I'm misreading something, the controller you're using already does exactly what you want if you simply set it to "step" firing mode. Unless you need more than 18 outputs, so you're driving 12 in sequence from just the one controller output while using other controller outputs for other things. Never mind - maybe I just answered my own question.

 

I'm confused; unless I'm misreading something, the controller you're using already does exactly what you want if you simply set it to "step" firing mode. Unless you need more than 18 outputs, so you're driving 12 in sequence from just the one controller output while using other controller outputs for other things. Never mind - maybe I just answered my own question.

You are correct in that I want to drive 12 in sequence from just one output.

 

First, this is not a site where you can have others engineer a circuit for you. Given my limited understanding of gates and counter applications, I'll post a drawing (because I enjoy a challenge from time to time). I'll let others pick apart my circuit as they see fit - being they probably have more experience and knowledge than me. Still, I've tried to anticipate every circumstance.

The circuit below consists of two CD4017 Decade Sequential Counters (U1 & U2), a Quad, TWO input NAND gate (U3), Relays (K1 through K12), R1 and Q1.

A few comments on my drawing: All relays are tied to a common point (the box) which DURING a clock pulse, GROUND is provided via U3a and Q1 (a PNP bi-polar transistor of your choosing). Otherwise, no relay can activate. Because only one relay can be active current draw is not excessive. During the LOW clock pulse ALL relays are off.

At U1 and U2, only output #0 will be high, which is not connected to anything. When the first clock pulse goes high U1 clocks from output #0 to output #1. At that time K1 (the relay) is energized. ONLY during the clock pulse does K1 also see ground. With the next clock pulse U1 switches to #2, and so on until the output reaches #9.

When U1#9 goes high U3b (pin a) is held high, enabling the clock pulse to pass through on U3b (pin b), inverting the clock pulse. U3c RE-inverts it back to original, thus avoiding any lag between K8 & K9. U1 is disabled while pin 9 is high, and U2 is clocked from #0 to #1. Count will continue until U2#5 triggers a massive reset. The whole system is now ready to repeat the function.

I gave no attention to your clock pulse because it sounds like you already have that figured out. Your question hinged on how to sequentially trigger relays. The schematic below is capable of triggering a maximum of 16 relays. The last pin output is needed to trigger the reset.

As for how you wire your relays, what power source you use for them - that's all up to you. This circuit only gives you the answer you originally asked. Are there other solutions? Probably. Would I personally use something other than a relay? Well, considering you're working with potential pyrotechnics, I think a relay, which offers a COMPLETE lack of power, would be a better choice.

Many years ago NASA was building a solid fuel rocket. They didn't want the ignitor going off accidentally so they shorted the igniter wires together. That solved the problem. Until someone discovered that static electricity could set off the fuel. So they decided that they would not only short the pins they would also ground them to prevent static from developing a potentially catastrophic accident (again). Live and learn. The key being on "LIVE".

Whatever you are triggering - the sequential relay system can give you a reliable ground AND power - I'll let you configure the relays however you see safe and fit.

On your timing of the circuits - you already are controlling the pulse width and duration. Keep in mind you shouldn't need a whole two seconds holding the relay on. You can shorten the cycle so you trigger a relay for (oh, lets say) 500 mS (Milli Seconds - 1/2 second), and trigger a pulse every 3 1/2 seconds (if you need four seconds between bursts). This will maximize your battery life by not holding a relay needlessly long. It only needs to be held on until it accomplishes its task

As for power: I built a similar circuit many years ago when we were flying model rockets. The trick was to be able to launch the rocket then make it to the recovery site quickly. That meant a whole lot of sprinting. So I built my delay circuit similar to what's drawn. The last few outputs triggered a car horn powered from a motor cycle battery just before the launch. I could be waiting down range with my children to recover the rocket. Using a motor cycle battery to power your circuit, relays AND fire off your pyrotechnics should give you plenty of power while keeping everything uniform. Plus, you can always recharge the battery with a charger OR even with solar power if you like (being outside in daylight).

 

Tonyr1084, thank you for your input. The model rocket circuit you implemented is really neat. My son and I had to use the sprinting method.

As far as relays, while they are used in the industry, there is some hesitance as there have been known cases where impact to the module could cause the contacts to "touch" leading to premature ignition. Devices such as the controller that I listed above use mosfets, but have to account for ESD to prevent the premature ignition, so they use redundant mosfets on both the high and low side.

 

Launch timer was a 555 with a clock pulse about every one second. That was driven to a Dual D Flip Flop, dividing my time by four. I could set for a 40 second launch window, enough time to jog and not sprint. The horn was driven by the clock signal, the 6th, 7th and 8th steps and by one of the D type flip flops. I'd get a one second blast every four seconds.

Launching off of a 9V battery was a hit or miss proposition, but with the 12 volt car battery I could make my own igniters, and they'd fire off every time. I don't remember the gauge wire I used for my igniters, but they were small. Burn out quickly and with a lot of intensity.

You're welcome for the circuit. Always nice to practice a trade I haven't messed with in a few years. (many years - I admit it). As for the relays banging contacts if dropped - that'd have to be quite a drop. I would have a plug in system where I wouldn't plug in the PT (PyroTechnics) until after I had the timer controller on the ground and grounded. And grounding the PT's I'd do so through a 1MΩ resistor just to make sure the act of plugging them in didn't set them off.

 

Relays with 5 A contacts to handle a 3 A load probably need more than 1.5 to 3.5 mA of coil current.

ak

 

Is it important that the switched output have rapid rise and fall times? Per your comment above about noise causing an unintended firing of a MOSFET output, a simple R-C filter on the gate can suppress this. The tradeoff is that the greater the suppression, the more slowly the FET turns on and off. But slowly is a relative term. A very slow 100 ms transition on the gate would appear as a 10 ms transition on the output. Does the load require the instantaneous snap of a relay contact closure, or are a few milliseconds ok?

ak

 

Is it important that the switched output have rapid rise and fall times? Per your comment above about noise causing an unintended firing of a MOSFET output, a simple R-C filter on the gate can suppress this. The tradeoff is that the greater the suppression, the more slowly the FET turns on and off. But slowly is a relative term. A very slow 100 ms transition on the gate would appear as a 10 ms transition on the output. Does the load require the instantaneous snap of a relay contact closure, or are a few milliseconds ok?

ak

A few milliseconds is no problem at all. Even hundreds of milliseconds would be ok if it is relatively consistent. The timing could be adjusted in the controller then.

 

Here is a basic distribution circuit based on relay outputs. Getting back to working on a FET version.

Notes:

1. This assumes an independent power supply.

2. This has a power-on reset built-in, so it can sit indefinitely between when it is powered up and when the first control pulse comes in.

3. This does *not* have protection against the continuity test pulse.

4. Note that U4 has two unused sections. These are used on the left side of the schematic as input signal conditioning. The part says 2003 because that's what's in my library.

ak

 

Prelim pass at a non-relay version. This might need better input noise/transient control, don't know enough about the environment. This one is powered directly from the DC power pulse being distributed. The first pulse fires up the circuit, the second pulse becomes output #1, etc. One pass through the outputs, no recirculation. Still no test current handling.

ak

 

New approach to the circuit on the way, better. Still need more information about the test pulse.

ak

 

AnalogKid, thank you so much for the schematics! I need some time to digest it all and try and understand all of it. I am sure I will have some questions.

I did get in touch with the manufacturer of the control unit to understand the output a little better. Here is what I got as a response:

When the control unit is sending out the test voltage to check for continuity of effects connected, it is current limited to around 25mA at 18V (2 9V batteries). And actually, all units produced after 6/1/2015 are current limited to around 5mA, but I have some units that are older. When sending the firing voltage, this current limitation is removed and can reach 3 to 4+ Amps at 18V (depending on the brand and quality of the batteries - Energizer Industrial is the recommended battery). They actually have the control unit listed in the manual at 18V and 6 Amps per output, but it depends of course on the number of effects connected (the load) to a single output (which is set to a specific number to ensure all effects go off). The control unit can be set to either send 100 millisecond pulses or 2 second pulses, meaning the time that they are "hot". The time in between is what I can program into the control unit. I have always used 2 second pulses exclusively to ensure the effects go off.