nte 2018 not working

[ChrisP58]

I know that all of the 4051 outputs are connected. What I was saying is that only the one output currently selected by the ABC address lines is actively being 'driven' since only that line is connected to the hard output of the 4060. The other 7 outputs are floating, not driven high or low. So they will float high, low, or may oscillate. Since that is the clock line of the 4017s, if they oscillate, you may may trip all of the outputs in the first few seconds of opperation.

Also, the 0 output of all of your 4017 is high even when you have everything in reset. That means that 8 of your igniters will fire as soon as you turn the power on.

For a counter I would probably choose a 74HC4040. But there is a problem with using an asynchronous counter in this type application, in that the outputs don't change states at exactly the same time like synchronous counters do. That means that you could get spurious values across the address lines each clock pulse. To combat this, take the clock signal and run it to one of the output enable lines of all of the output decoders. Choose the state such that the selected output is only on when the clock line is LOW.

The resulting timing will be: All off - Q1 - all off - Q2 - all off - Q3, etc.

You could also use a synchronous counter, such as a pair of HC161s, but I'd still recommend using the clock line to disable all outputs for half of each clock period.

 

[ebb]

so should I put a resistor in series with the 4051 output and the 4017 clk. so you are saying go to the pin 13 which is the disable pin on the 4017. also would the 74hc4040 be replacing the 4017

 

[ChrisP58]

A 10K resistor from each clock pin to ground.

But that won't fix the problem of all of the Q0 outputs of the 4017 being high at reset, and until each 4017 gets clocked away from zero. That fix will take adding another 4017 and not using Q0 from any of the 4017s.

 

[ebb]

would you replace the 4017 with the 74hc4040

 

[ChrisP58]

The HC4040 would replace the counter part of the 4017s. 10 of the HC238s would replace the decode part of the 4017s. You will also need a couple more 138s or 238s for intermediate decoding.

The 8 outputs of the 238s will drive the 8 inputs of the ULN2803s.

 

[ebb]

now I am getting confused. so the 4040 will not replace the 4014 it will just replace the counter part. does the 4040 with each clk input move to the next output

 

[ebb]

how about this circuit will still have the same amount of outputs as last circuit just cut it down to save time

 

[ChrisP58]

No, that won't work. You only need a single 4040 in the whole thing.

A single counter that will count from 0 to 79 in binary. Then decoder logic to select one of your 80 individual outputs for each count.

Do some research on binary numbers to understand them and how they work.

 

[ebb]

I know the binary from school just having a hard time triing to figure out the circuit you are talking about. got the first 7 outputs but from there I gets all messed up

 

[ChrisP58]

This should do what you need.

Of the counter outputs:
- Q1, Q2 and Q3 select which one of the 8 outputs of the HC238 go high.
- Q4, Q5 , Q6 and Q7 select which one of the HC238's get enabled.
- Q8, low to begin with, will disable all outputs when it goes high at the 80th clock pulse. All outputs will stay off for the next 79 clocks, then will start over from output 00.

View attachment Decode-80.pdf

 

[ebb]

thank you chrisp58 the only question I have is it says 5v logic. am I able to still use 12v on the 2803 to fire the talons

 

[ChrisP58]

The ULN2803 can handle up to 50Volts on it's output, even when it's input is driven with 5Volts.

 

[ebb]

been looking at the datasheets whats the difference between the 238 and the 138

 

[ChrisP58]

The difference is the state of the outputs.

The outputs of the HC138 are normally high, with the selected output going low. The HC238 outputs are normally low, with the selected output going high.

 

[ebb]

this is the drawing of that circuit you sent me the only thing is I cant find the 74hc238 on my eagle software

 

[ChrisP58]

The pinout is the same for both the 138 and 238. The symbol difference is only that the 238 won't have bubbles on the outputs.

Make sure that all input pin are tied either to another output, or +5v or ground. No logic inputs may be left floating!!!!

You will need to add decoupling caps to the layout.

Your schematic shows the ULN2801. If that is what you will be using you need to add a 2.7K resister in series with each ULN2801 input. The ULN2803 already has that resistor.

You can replace the two hc138 parts with a single HC42 decade decoder.

 

[ebb]

what is the full part # for the hc42 is it 74hc42

 

[audioguru]

The datasheet from Texas Instruments is found on www.datasheetarchive.com with the part number SN74HC42.

 

[ebb]

ok 1 question what is You will need to add decoupling caps to the layout.

 

[ebb]

hi chris
its been a while but in the conversation about the 2018 you said I need decopling caps just wondering where I need the and how do I go and replace the 2 138n with the decade counter
thanks eric