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I don't get the whole picture here, so let's see if I have this correct... The 4017's are located on your own board at the end of a long ethernet cable connected connected to this relay interface board?

Please explain in detail what the relay interface board does, what your 4017 board does, how they are connected together, how they are powered, and what lengths of cable are used. Unless you do that we'll all be going around in circles.

Dave.

Now I *am* confused. When you posted that pic, I expect we all took it to be the board you were using.

That board uses 12V for relay coil supply:

The 2803 type drivers are open collector (and typically specified for 30 volts or so).

So can you explain again where this Kits'r'us board fits into your scheme?

The printer port puts out TTL compatible voltage levels and will not reliably clock a 4017 powered from 12V. The 4017 will have problems driving the typical relay coil directly. You should forget about completing this project on time and ask your teacher for an extension. You have a lot more homework and circuit modifications to perform before you get close to finishing it.

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Hopefully these pics will show the full set up.

This is the inside of the firing box. The barrier strip at the top brings the +12V and ground for the firing control boards (at bottom) as well as a separate ground for the igniters that is controlled by a safety switch. I added the cap to the barrier strip last night in an attempt to help stiffen the power supply to be boards, but have not yet tested it.

The second pic is the top side of one firing control board. There are

5 of these in total. The IC at the top is the 4017. The black rectangular boxes at the bottom of the board are the SPST reed relays that activate the igniters.

The underside of the firing board. The wide trace on the right side of the board is the +12V and the left side is ground. Are these too small?

This is the Kit74 parallel port interface as well as the power supply. I only have them sitting this close in order to fit them into one picture. I have wired leads onto the Kit74 that goes to an RJ45 jack. That ethernet cable then goes to an identical jack where each line is connected to the clock pin of one firing control board.

So in theory the operation goes like this: The system is powered up and all counters and parallel port are reset. The ignitor ground is then connected via a remote switch.

intervals activates a single channel output on the parallel port. That signal is then sent from the Kit74 interface via an ethernet cable to the firing boards in the display. The 4017 in the firing controller advances one count, activating the next relay in line. The wire connected to the relay receives +12v which passes through the nichrome igniter and returns to ground through the safety switch. The wire heats, igniting the fireworks. The igniter typically burns up in less than 1 second. The process repeats until all 9 cues have been used.

The thing that confuses me is that in tests that I ran last week, the system worked fine with only a test load. The clock pulses generated by the Kit74 advanced the 4017 one step each time with zero errors. I used the exact equipment I am now, including the ethernet cable to deliver the clock pulses. It wasn't until I installed it into the firing setup and did a test with an actual igniter that these problems began to occur. After I increased the wire gauge for the power supply to the firing boards, it had enough power to fire the igniters, but began skipping steps and was far more susceptable to any sort of interference. Even checking the power supply lines with a DVOM was enough to move the counter several steps.

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Schematic showing how the 4017 is driving relay would help.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
         America: Land of the Free, Because of the Brave

Where are you taking the pulses off the kit74 board? That board has eight relay outputs, and possibly eight open collector outputs. It would not be a good thing to use a relay closure to generate the clock pulse for your 4017. We are starting to suspect that your 4017 interface to the e-match drive relays is inadequate. The 4017 has a high output impedance and cannot maintain 12V at its output except for maybe a few hundred microamperes loading. Your relays are almost certainly several

10's of milliamps loading, this will load the 4017 output to something less than 8 volts and the relay will not activate.

I've soldered leads onto the resistors on the kit74. So (as best I can tell), I'm getting the signal out of the 2018 directly. I initially was going to use the relays, but could not find a suitable debounce solution so I opted instead to go right to the amplified output of the 2018. Up until I put a full load on the relays, everything worked fine. Which to me is the confusing part (which I'm sure is 99% my inexperience combined with ignorance). If the setup will work fine when the only load on the relay is an LED, then why do you suspect that the 4017 is unable to power the relays? My understanding (again, probably wrong) is that the 2018 is basically 8 transistors grouped together on a single IC. They take the 5 volt input from the parallel port and reproduce the same signal with a 12 volt supply. At that point a pulldown resistor keeps the clock pin on the 4017 low until a 12 volt signal is received via the 2018. When the 12 volt signal is removed, then the 4017 sees that as one complete clock pulse and advances to the next output. In practice, this model has seemed to work. The firing control board will move one step per pulse from the 2018 which is verified both by the LED indicator on the board as well as an LED attached to the lead that runs from the relay to the igniter.

At this point in the day, it's looking like I'm going to have to go to plan B. But this process has definently been a learning experience, and I'd like to continue that, even if it means not finding success until next 4th of July.

Thanks everyone for all of your help on this. I certainly wish I'd found this group sooner, probably would have saved myself a lot of trial & error and subsequent headaches ;)

Okay- that part is okay, except the 4017 advances on the low-to-high transition of its clock input. When you address the wired output on the kit74, that output pulls low, and when you de-address it, the output returns to a quiescent high and triggers the 4017. Generally, logic circuits are not used to drive relay coils. We usually use some kind of buffer like so: View in a fixed-width font such as Courier.

.. . . . . +12V . | . .-----+--o-. . | | | . | - | . 1n4001 - |/| < . ^ |/| | . | |/| '--o---> to ignitor . | - . | | . '-----+ . | . | . |/ 2n2222a . 4017 >---[10k]--| or . output |> 2n3904 . | . | . --- . gnd .

Something like this will avoid that quirky behavior you were seeing...

That would be best.

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Problems:

1) You are driving the relays directly with a 4017, that's *bad*. A 4017 will not have enough output current to do that. You are using low power reed relays, but it's still too much for a 4017.

2) You can't use a relay driver board to provide clock pulses to a

4017, in fact this probably the worst possible way I can think of to do this. You'll get ridiculous amounts of contact bounces causing multiple pluses.

3) You are feeding power to the remote boards via the long ethernet cable that is also the same ground line as the 4017. Power for the

4017 board should be local.

I'm surprised it even worked at all with no load.

At the very least, this might help until you can design the whole thing properly from scratch - add a single-shot circuit to the 4017 board clock input so you are guaranteed to only generate one clock pulse from how ever many erroneous input pulses.

Dave.

David L. Jones wrote in sci.electronics.design:

[...]

I've always taken for granted (meaning I never checked) that reed contacts don't bounce. Not that that would make them an appropriate device for clock generation.

Anno

The voltage to the 4017 is drooping due to the current drawn by the igniter, and a spike is bing introduced. You need to isolate the supply to the 4017 from the voltage droop and spikes caused by the igniters. That is the _first_ step, and you may not need to do anything else. Add a diode and 2 caps as shown:

----o----igniter---gnd Vsupply + ---+------------}}------------o---^ | Igniter relay \\ / D1 contact ---- | +-------+---Vcc to 4017 | + | [470uF] [.1uf] | | Gnd ---------+-------+

The above shows only a partial schematic for the addition of caps & diode. You may need to do other things, but if the igniters and the 4017 share the same supply, you must do the above as the first step.

Ed

After I increased the wire gauge for the power supply

Dry reed relays bounce like any other relay. The special mercury wetted type do not. The relays on the OP's parrallel port providing the clock pulse are not reed, let alone mercury wetted.

Dave.

use a separate supply to run the ignitors to the one that runs the logic and relays. Or put a diode before the logic and use a large capaciror across the logic supply.

Bye. Jasen