4017 count to 20

[pyrohaz]

Hi guys,
I need 20 inputs to my arduino simple. I'm using mosfets to switch the inputs (already devised the circuit and tested, that works fine!) All I need to know is:

How can I use two decade counters to count to 20? I know I could do this with 3 shift registers clocking 1 bit in and shifting it up 20 bits but that would require 3 chips and 2 decade counters only require a reset and clock.

Anyone know the answer?

Cheers,
Harris

 

[(*steve*)]

Look at the 4017 datasheet, I'm pretty sure it has a circuit to do just this.

However a number of 74HC165's is probably better if you want digital inputs as you won't have to have all those mosfets.

 

[CocaCola]

I would just program and slave another micro to do it, that is if I was looking to save parts count on an existing design or platform...

 

[pyrohaz]

Look at the 4017 datasheet, I'm pretty sure it has a circuit to do just this.

However a number of 74HC165's is probably better if you want digital inputs as you won't have to have all those mosfets.

Thanks for the reply, i'm not actually reading a digital input, i'm using the mosfets to really shoddily multiplex 20 capacitors into a 555 timer (a weird form of DCO I suppose). By seeing the frequency of each capacitor I can get a very rough estimate of capacitance.

Hence why using another micro would be a bit annoying as it would literally only be doing what 2 decade counters would be doing, and i'd have to buy another chip!

 

[BobK]

Please explain exactly what you are trying to accomplish. You posts scream that you are making something more difficult than it is.

Bob

 

[pyrohaz]

Happily!

What i'm trying to do is find a method of multiplexing lots of capacitive switches, going off the ESD model, a human can be modelled as a 100pF capacitor in series with a 1.5k resistor. What I have thought is to have a free running oscillator with the output in series with a resistor. Mosfets are used to couple this output to each touch switch/pad where if the pad is touched, it has capacitance, if not, it has a smaller capacitance.

By then doing this, the amplitude of the signal can be detected using a single peak detector circuit and by running through each mosfet and subsequently reading each input, can detect whether the input is being pressed or not.

Is there a better way to multiplex many capacitive inputs? This method only required 3 pins!
(Analog read, clock and reset, reset isn't completely required, just adds the option to start at zero again).

 

[sheldonstv]

here you go-easy to alter this circuit to have as many outputs as you want by using the last op as a reset-remember each additional ic gives only 8 usable outputs.....