Non-Contact Voltage Detector

Log in or register to post comments
Go To Last Post
10 posts / 0 new
Author
Message
JimutD
JimutD's picture
Level: Hangaround
Joined: Thu. Jun 27, 2013
Posts: 193 View posts
Location: India
#1
Posted by JimutD: Sat. Oct 11, 2014 - 04:50 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I made this one in the sim using schmitt triger. I found many sources but with odd resistor values. But the sim is showing different results.

The first problem is when using 3V supply everything is getting flat after A2, so output is 0V. This was obvious because the max voltage of the schmitt triger was 1V so I changed the supply to 1V and the problem was happening between A2 and A3, the functionality of this part is to keep the voltage above the threshold voltage of the trigger or something I may not know. It is not doing that, so the output is again 0.

Blue is after A2 and green is before A3.

As shown here in https://www.youtube.com/watch?v=AWlRGLxm7nc that should be like this

What is the problem in my circuit? I mean using resistors between 1M and 1R

This topic has a solution.

Tags:

Learning and Information, General Electronics
Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 22970 View posts
Location: Melbourne,Australia
Posted by Kartman: Sat. Oct 11, 2014 - 10:42 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You're going to loose 0.7V across a real diode then 1/10th due to the 2k/22k divider. So your circuit will not work for 1V. What schmitt inverters are you using? 74HC14 would be a good choice. 

Top
JimutD
JimutD's picture
Level: Hangaround
Joined: Thu. Jun 27, 2013
Posts: 193 View posts
Location: India
Posted by JimutD: Sun. Oct 12, 2014 - 07:36 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Exactly, I am using 74HC14. So you are saying with these resistor values it would work with 3V?

Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 22970 View posts
Location: Melbourne,Australia
Posted by Kartman: Sun. Oct 12, 2014 - 09:33 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

How did you come up with the 2k and 22k resistor values? How does the time constant work out with 100nF?

If you like guessing, then try different values. You have a simulator.

Top
JimutD
JimutD's picture
Level: Hangaround
Joined: Thu. Jun 27, 2013
Posts: 193 View posts
Location: India
Posted by JimutD: Sun. Oct 12, 2014 - 03:23 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I am not understanding that part, I found the values from another video. If you tell me the function of it I may guess something out.

Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 22970 View posts
Location: Melbourne,Australia
Posted by Kartman: Sun. Oct 12, 2014 - 09:20 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'm assuming you are an electronics student since you seem to be able to work the simulator. So, i'm assuming you have a grasp of the basics like ohms law. If not, there are plenty of tutorials on line to give you a grounding. Much better than i can achieve here.

given your simulation results, we can see your capacitor doesn't charge much past half vcc. Thus decrease the 2k resistor. 

If you read the datasheet of the 74hc14 it will tell you the expected output voltage for a given VCC and what the high and low voltage levels are. 

 

The 22k resistor is to discharge the capacitor. Google rc time constant

Top
JimutD
JimutD's picture
Level: Hangaround
Joined: Thu. Jun 27, 2013
Posts: 193 View posts
Location: India
Posted by JimutD: Tue. Oct 14, 2014 - 10:06 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ok, I found that 560K and 100nF holds the perfect time constant for me and reducing the value of the charging resistor to 1R. It worked perfectly in the sim. But did it in breadboard and it is not working.

As I was doing with 3V supply voltage I thought there may be some changes due to it, so I copied this circuit and did it on breadboard and it is still not working as it should be, not even detecting static energy of my hand or any 220V line.

 

And I am a computer science student.

Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 22970 View posts
Location: Melbourne,Australia
Posted by Kartman: Tue. Oct 14, 2014 - 11:33 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You went for some extreme values. The idea is that it takes a few cycles to charge the capacitor. If t=rc then the capacitor charges in 100 nano seconds. Way too fast to be useful. 

I dare say you've made your circuit wrong or you're the undead. Dead people or zombies won't be detected by this circuit. Seriously, you need to do some measurements. Electricity is invisible to the average person, for zombies it might be different but i don't know any zombies. Communication would be problematic methinks. You pc sound card can be made into a half useful oscilloscope. Let google be your guide. Moving forward, befriend an electronics student, between the both of you the combined skills should benefit both parties. Even better if she is a hot chick - but she might treat you with disrespect or secretly be a zombie - beware!

 

Top
JimutD
JimutD's picture
Level: Hangaround
Joined: Thu. Jun 27, 2013
Posts: 193 View posts
Location: India
Posted by JimutD: Tue. Oct 21, 2014 - 05:35 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ok, I solved it. I used the half useful oscilloscope, and found the problem was something with my work table. It is awkward I know, but projects related to this type of thing (like I have tried capacitive touch sensing lately) dose't work on this work table. It am still in search for this reason but hopefully there is no zombie here in my table.

I tried on the same thing on the same breadboard everything was same except the table it worked. But still not detecting my hand's static energy. Anyways that's not a problem, it is detecting AC voltages.

I am really getting confused in this kind of things. When my laptop is connected to the ground (through charger) and thus the voltage detector through sound card, it is detecting my static energy. But when on battery it is only detecting AC voltages. Where the problem with the table persists.

Top
Kartman
Kartman's picture
Level: 10k+ Postman
Joined: Thu. Dec 30, 2004
Posts: 22970 View posts
Location: Melbourne,Australia
This reply has been marked as the solution. 
Posted by Kartman: Wed. Oct 22, 2014 - 01:21 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Nothing to do with 'static energy'. It doesn't work by static electricity - the body works as an antenna for 50/60Hz

Top