I would prefer breaking anode V supply as shown on my schematic. Remember that 4017 output # 1 stays high on reset.

 

Bernard, that's a very interesting comment you just made regarding the 4017 outputs. I'm using two 4017's in this circuit, call them 4017A and 4017B. 4017A has eight outputs available (Q0 and Q9 are used to reset and cascade to 4017B via a 4081). The SCR's that I'm having this problem with are all controlled by clock pulses from 4017B. Some of the outputs on 4017B are not connected to anything. Should unused 4017 outputs be grounded?
Another thing I just realized - I'm using just one of the gates on the 4081 that's between the two 4017's but I don't think I have the unused inputs grounded. I'll bet that one or both of these things are the root cause of the LED issue. Your thoughts?
Regarding which rail to interrupt for SCR resetting, I can wire it either way, no problem.

 

I checked the wiring and I do have the unused inputs on the 4081 that's between the two 4017's wired to ground, but I didn't use a resistor - the inputs are wired directly to the ground rail. On 4017B I'm using Q1, 2, 3 and 4 to operate the relays. The remaining outputs are definitely not connected to anything.

 

I've done more digging and found some info regarding putting resistors on the 4017 outputs when using it to sequence LEDs. The article said that damage to the 4017 output pins may occur without these resistors (no resistor value given in the article). Depending on the 4017's supply voltage, current-limiting resistors for the LEDs would probably be needed anyway.
I'm using the 4017's to power relays with 740 ohm coil resistance. The supply voltage is 12VDC, so that works out to 16mA at the outputs if I did the calculation right (V/R = A). This seems a bit high, and I can reduce the current to 2mA at the outputs by placing 5K resistors in series to the relay coils. I'm still on the uphill slope of the learning curve when it comes to IC circuit design - am I on the right track here? Should I be considering using transistors at the 4017 ouputs to drive the relays?

 

I show several such schematics in that article complete with resistors. Figure you want to limit current to an absolute no more than 10ma, the chips rated specs are 6.8ma.

This design is one of my favorites, I've build several. I don't remember if you are wanting to do a simple sequence or a fancy pattern, but even with steering diodes it should work OK. By not using drivers the chip is at risk though, which is why I also showed transistor drivers on other schematics. Wookie and I go about this very differently.

Chapter 9

The 4022 and 4017 are kissing cousins, both are Johnson Counters, the 4022 just has fewer outputs.

 

Thanks, Bill, for your input. I'll check your e-book entries.
I went back and checked the signals going to the 4081 inputs for channel 2. If I configure the circuit to send just one signal to the 4081 at input 2A (from the 4017) OUT2 doesn't show any voltage going to the SCR gate pin. The 2B input still has a physical connection to the other input source, a 12VDC signal that's switched by the relay, but there is no voltage signal being sent through the wire in this instance. Now, if the 4081 gets high signals on both 1A and 1B (triggering it's SCR and lighting LED1), then LED2 will light with only a single high input, the one from the 4017. If only one input signal is sent to channel 1 of the 4081, then LED2 does not light. I know I keep describing this problem in my posts (apologies) but it's driving me up a wall.
I'm going to try the current-limiting resistors in series from the 4017 outputs to the relay coils - I calculate that a 2K will result in a 6mA draw on the 4017 outputs. I've a number of fixes for this; at least I'm learning what doesn't work LOL. More to come...

 

Please no not ground outputs. 4017 outputs can be loaded beyond specs but then the output does not meet spec as output V falls with increased loading. With 12V supply, high out, 2.7mA gives 11V out; 4.7 mA= 10.5V; 10.9 mA = 9.5V; 17.5 mA = 7.7 V. Why are you using relays? I hooked up the circuit on a multi socket proto-board, 555, 4022, 4081, 2n5060.& red LED.; all worked as suposed to. Do you have diodes across relay coils? Short of sending it to me , do not know what to say.

 

Hi Bernard,
I wasn't planning to ground the 4017 outputs, just trying to reduce the current required from the 4017 outputs to energize the relay coils. I'll leave the unused 4017 outputs unconnected.I'm using DPDT relays to switch two circuits when the relay turns on. One set of pins is for a small incandescent lamp that heats the TC junction that I need to test. The other sends the TC signal to an amplifier to boost the mV signal up to ~1.5VDC at room temp (~18° C.)
That's good news that your test circuit is working - thanks for taking the time to check the design. I still have to check one more thing, which is removing the OUT2 wire from the 4081 to SCR1 and see if the LED still lights when the 4017 cycles to that gate.
Another thing I suspect is that the relays are somehow sending a spike over to the SCRs, the 4081 or the LEDs power rail and causing the problem. I do have 1N4148 diodes across the relay coil pins. If I still have the issue after pulling off that OUT2 wire, I'm going to replace the relays with 2N2222's and see what happens.

 

Whew! Finally found the problem. I put the board on the 'scope and checked the outputs. I found that the relay wasn't releasing it's contacts when the 4017 clocked to the next output pin. The overrun was just ~7.5 ms but that's enough to trigger the 4081 gate and latch the SCR. I pulled the relay from one of the 12 channels and installed a 2N2222 with a 1K base resistor and the overrun problem vanished. I am getting quite a bit of oscillation, though, on the signal going through that transistor. I'll do more homework on that issue, but for now the circuit seems to be stable and working as designed. Thanks to all who gave advice - I learned a lot while working through this thing.

 

Can you post a schematic of your current circuit that works, but that you are getting oscillation on?

May as well get it right, the oscillations could cause further problems down the road, leading people to ignore a false alarm or similar.

 

I'll be working on the schematics (drawings, actually) on Monday. I'll post as soon as I have them completed.

 

This was litorally cut n paste, but may be of some help with your master drawing.Bill's power up reset is included. On reset, first 4017 Q0 goes high resetting second 4017. Skip Q 0 & start with Q1.Instead of resetting first 4017 at full count , clock enable is inhibited, stopping operations untill power is interupted. the NAND gate inputting to first 4017 clock enable is a negative NOR, to keep from introducing another IC type. Any questions, keep asking ,maybe we,ll get it right someday, but for now it,s late & I,ve got a bug.