cd4017 counter to 8 lines instead of 10

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neazoi

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74hct4017 counter to 8 lines instead of 10

Hello,
I need to use a 74hct4017 as a serial driven band pass bilter switching means. I need only 8 outputs instead of 10, how can these be done?
 

I need only 8 outputs instead of 10, how can these be done?
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I guess you mean count modulo 8 instead of 10?

That's quite easy by wiring the reset input respectively, I'm sure you'll figure it out.
 

FvM said:
I guess you mean count modulo 8 instead of 10?

That's quite easy by wiring the reset input respectively, I'm sure you'll figure it out.
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You connect the 9th output to the reset input? but then you have a spare pulse (the 9th) that is not switching anything, it does just reset. Can it be done without this extra pulse? (switch back to 1 directly)
 

Can it be done without this extra pulse? (switch back to 1 directly)
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Yes, by using a 1:8 johnson counter CD4022.

I don't believe that a short switching delay from output 8 to 1 is any problem in your application. Can it be that you have difficulties to distinguish between essential circuit function and peripheral effects?
 


The 4022 is what I was looking for. No extra pulse and no extra hardware required.
I think it is not TTL levels compatible, and as far as I can see there is not a 74hct4022.
My relays need 5v for the ONE state and I am using a ULN2803 as a driver. Any ideas of how to do it?
I believe if vcc to the cchip is 5v its outputs will be 5v in the high state, am I right?
 
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Relay control is an application where the previously suggested asynchronous 4017 reset circuit will work without any problems. So you are free to use 4017 or 4022 type at will. I believe there are also 74HC4022 types, but probably not sold in a DIY shop next door.

The drive strength and speed of classical 15V CD4000 with 5V supply is much lower than 74HC types, but always sufficient for a 2803 driver. 74HCT would be necessary if your input logic high level is below 3.5 V, e.g. when old TTL logic or MOS processors are driving the circuit.
 
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    neazoi

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More important than speed in my application is the output level, which is required to be about 5v for the ONE state. The inputs to the counter will be from the PC LPT so they will be about 5v for logic 1. The outputs of the counter will go to a ULN2803.
Will it be sufficiend to put a vcc of 5v to the counter to drive the 5v relays in this configuration?
 

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