Hmm... Decade counter stops counting

[kuksul08]

I need some advice.

I built this schematic a few months ago:

http://that.homepage.dk/EVS/

It works great on my desk using a 12V power supply. The 555 timer outputs with a frequency based on the variable resistor R1.

The problem is, when I attach it to my car (measured 14.15V at the terminal with engine on), it works for a few moments, then it stops counting. The 555 still outputs the signal, but the IC2 is stuck. The first time it happened, it stopped working completely. I re-built the circuit with new parts, and this time both banks remained on.

I measured with my DMM - at 14 I get the input from the 555. Q0-Q9 read the source voltage. All other terminals are connected properly.


This leads me to believe there is internal damage to that component - something is happening when I have the engine on that damages it. Can anyone help diagnose this issue? I'm not sure what to do now.

 

[kuksul08]

I should add - the counter I am using is
http://search.digikey.com/scripts/D...ang=en&site=us&keywords=568-2847-5-ND&x=0&y=0

 

[65535]

In my experience the DC in a car is very dirty, full of high frequency interference from the alternator. You'll want to use filter your line in with caps. or a shunt. Hope that saves future parts.

 

[TorchBoy]

I see you have two Q1 and two Q2. But (unless it's a heat issue because of the extra voltage) I'm only here to learn. :popcorn:

Edit:

You'll want to use filter your line in with caps.

What's the value of C1?

 

[kuksul08]

In my experience the DC in a car is very dirty, full of high frequency interference from the alternator. You'll want to use filter your line in with caps. or a shunt. Hope that saves future parts.

Yes I was thinking about this. I thought that C1 acted as a filter though. (a shunt is?)

I have considered using an LM317 that I have just to keep the voltage constant.

I see you have two Q1 and two Q2. But (unless it's a heat issue because of the extra voltage) I'm only here to learn. :popcorn:

Edit:


What's the value of C1?

I immediately thought heat - but it is located in a place where it stays cool.

C1 is 470uF with a 25V rating.

I may have just answered my own question. The counter I used is rated -0.5V-7.0V. No wonder it explodes when I put 14.1V on it. That is, the 'source' voltage it sees in this circuit is my 14.1V, correct?

from NXP datasheet for 4017 counter:

 

[VidPro]

yes

the capacitor is a bit of a filter indeed, but not much of one. if you loose the power-in legs with some resistance, then your capacitor will be able to filter the curcuit area better, and not attempt to filter the whole car :-)
but i just guess and hope :-) see how the capcitor is across the whole 12V line. with a bit of resistance added from the 12v line, that will seperate the curcuit side a bit from the "mains" then your filter there will clean up the lesser without trying to clean up the whole cars main.


you probably could just add in some resistance and check the voltage and have it close enough. even though the 555 itself handles the higher voltages (15v), i wouldnt trust it at those voltages either.
Because it dont use diddle for power to begin with, a simple locked 5v voltage regulator would not even have to be heat synced. would be to easy to add that or a adjustable voltage regulation. and that would Also provide a bit of a detachment from the rest of the car (resistance) and then your capacitor will filter the curcuit area more (as unnessiarily stated above)

5v locked reg because they sell that locally, and both of them will work with that, and then its easier, less things.

 

[TorchBoy]

Um, yeah. 14+ V for a 7 V max chip wouldn't be nice for it. You're talking of a 4017 counter and a 555 counter. :confused: What are IC1 and IC2? Edit - looked them up. IC1 = 555 and IC2 = 4017. Right?

I thought that C1 acted as a filter though. ... C1 is 470uF with a 25V rating.

I think a ceramic disk capacitor of a few picofarads might work better as a filter for transients.

 

[kuksul08]

Um, yeah. 14+ V for a 7 V max chip wouldn't be nice for it. You're talking of a 4017 counter and a 555 counter. :confused: What are IC1 and IC2? Edit - looked them up. IC1 = 555 and IC2 = 4017. Right?

yep :)

I think a ceramic disk capacitor of a few picofarads might work better as a filter for transients.

I'm not sure how that capacitance is selected or how the capacitor type affects it. I am using an aluminum electrolytic cap now.

 

[Mr Happy]

The idea of filter capacitors is not to smooth the supply so much as to bypass transients around the device. A capacitor acts as a kind of short circuit to AC signals so any noise in the supply tends to follow the path of least resistance through the capacitor and not enter the device being powered.

Also large value electrolytic capacitors may present a significantly increased impedance to high frequencies, making their effective value less than the label says. Usually a bypass capacitor would be about 0.1 to 1.0 uF tantalum, up to say 10 uF aluminum electrolytic. But most of the time, 0.1 uF is enough. The capacitor should be attached as close to the power supply legs of the IC as possible.

Regarding the over voltage thing, devices tend to fall into two categories: transistor level and logic level. Transistor level devices may be happy up to 24 V or more, whereas logic level devices are usually designed for a nominal 5 V supply and really don't like anything higher.

 

[HKJ]

I may have just answered my own question. The counter I used is rated -0.5V-7.0V. No wonder it explodes when I put 14.1V on it. That is, the 'source' voltage it sees in this circuit is my 14.1V, correct?

You cold try locating a 4017 counter, instead of using the 74HCT4017 counter. The 4017 counter will work at 12 to 15 volt volt.

The other options is to use a 7805 regulator to supply the two IC's, but then you need to adjust the value of R2 and R3.

 

[kuksul08]

The idea of filter capacitors is not to smooth the supply so much as to bypass transients around the device. A capacitor acts as a kind of short circuit to AC signals so any noise in the supply tends to follow the path of least resistance through the capacitor and not enter the device being powered.

Also large value electrolytic capacitors may present a significantly increased impedance to high frequencies, making their effective value less than the label says. Usually a bypass capacitor would be about 0.1 to 1.0 uF tantalum, up to say 10 uF aluminum electrolytic. But most of the time, 0.1 uF is enough. The capacitor should be attached as close to the power supply legs of the IC as possible.

Regarding the over voltage thing, devices tend to fall into two categories: transistor level and logic level. Transistor level devices may be happy up to 24 V or more, whereas logic level devices are usually designed for a nominal 5 V supply and really don't like anything higher.

I mostly understood this. Thanks

You cold try locating a 4017 counter, instead of using the 74HCT4017 counter. The 4017 counter will work at 12 to 15 volt volt.

The other options is to use a 7805 regulator to supply the two IC's, but then you need to adjust the value of R2 and R3.

I found this one, rated for 3 to 18 volts

http://search.digikey.com/scripts/D...7-5-ND&itemSeq=84726555&uq=634062041281866740

I'm hoping it's as simple as this :)

 

[TorchBoy]

What voltage is your particular 555 timer rated for?

 

[kuksul08]

What voltage is your particular 555 timer rated for?

It's this one: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-1411-5-ND

...rated for 18V max, so it should be fine.