Resistor Detection Circuit

Thread Starter

ConnaTC

Joined Jun 20, 2020
18
The 470K resistance is coming from the Phone socket.

The circuit will read the type of Circuit it is testing either there is a socket on it (470k) or It is a open circuit or a Short

If an Open Circuit or Short can’t be done or is a problematic to design i will settle with it just detecting the resistor.
 

KMoffett

Joined Dec 19, 2007
2,902
The 470K resistance is coming from the Phone socket.

The circuit will read the type of Circuit it is testing either there is a socket on it (470k) or It is a open circuit or a Short

If an Open Circuit or Short can’t be done or is a problematic to design i will settle with it just detecting the resistor.
The 470K 1% in my circuit is in the black box. It is half of the half bridge . The other half is your 470K in the socket. The three states could be Red LED (<470K - the tolerance), Green LED (470K +/- the tolerance) and Yellow LED (>470K + the tolerance). Or your choice of colors. ;)
PICAXE site

Picaxe08M_3LED.png
 
Last edited:

MrChips

Joined Oct 2, 2009
21,826
Here you go.
Rx is your resistor under test.
Both LEDs must be on for good resistor.
Adjust R1 to suit.

VDD - pin 14
GND - pin 7

Resistance Checker.jpg
 

Tonyr1084

Joined Sep 24, 2015
5,039
The 470K resistance is coming from the Phone socket.

The circuit will read the type of Circuit it is testing either there is a socket on it (470k) or It is a open circuit or a Short

If an Open Circuit or Short can’t be done or is a problematic to design i will settle with it just detecting the resistor.
I've never heard of a socket with 470KΩ resistance. Are you plugging something into that socket? Something that has a 470KΩ resistor built in? is this for testing a phone line?
 

LesJones

Joined Jan 8, 2017
2,696
If you need to test the value of the 470 K resistor in a phone master socket why do you not also need to test rge capacitor in the socket ? It would be a GREAT help if you give some details of the situation that requires this test. (For example items coming off a production line, testing bought in sockets from suppliers, testing new installations, diagnosing fault calls from customers etc.)

Les.
 

MisterBill2

Joined Jan 23, 2018
6,997
I've never heard of a socket with 470KΩ resistance. Are you plugging something into that socket? Something that has a 470KΩ resistor built in? is this for testing a phone line?
In other parts of the world telephone systems are a bit different and in one area there is a 470K resistor between two of the terminals on a phone jack. So this thread was asking for a simple way to verify the presence or absence of such a resistor.
This application was not described initially and as a result all sorts of wild suggestions appeared. What was never mentioned was the skill level of those doing the checking. Some could do it very well with the digital multi-meter shown in post #12, while those with a lesser skill level would be hopelessly confused just looking at that meter.
Once again a question has been posed without an adequate explanation of the context.
 

Tonyr1084

Joined Sep 24, 2015
5,039
Once again a question has been posed without an adequate explanation of the context.
It would seem so.

I guess nobody wants to divulge the next multi-million dollar idea. But electronics is a very specific field. Once, working at the counter of an electronics wholesale outlet, some guy came in and asked for a cable that plugs into the back of a thing and the back of another thing. He had no idea what it was called. So I told him 'I'm not sure of the name, but we don't carry it. Try XYZ down the street. I'm sure they can help you.' The customer happily left. And I don't recall him ever returning.

Some come here wanting free engineering services. Simple circuits - that's easy enough. But when they want to know how to control something in a complex way but don't want to give away what they're doing with it, they're not going to get the kind of help they want.

Where I live, I've never seen, or even heard of a resistor built into a phone socket. That doesn't mean there isn't any, just something I needed greater clarification. Thanks Mr. Bill, for clarifying that. Now we have to assume the 470KΩ is no greater than a 20% accuracy. Unless someone knows better. I still don't think the TS has said what the precision level of the resistor is. I'll have to look back through the entire thread to see. I DO recall some saying what values they can expect at 20, 10, 5 and 1%. But I don't recall a specific answer to that question.
 

MisterBill2

Joined Jan 23, 2018
6,997
It would seem so.

I guess nobody wants to divulge the next multi-million dollar idea. But electronics is a very specific field. Once, working at the counter of an electronics wholesale outlet, some guy came in and asked for a cable that plugs into the back of a thing and the back of another thing. He had no idea what it was called. So I told him 'I'm not sure of the name, but we don't carry it. Try XYZ down the street. I'm sure they can help you.' The customer happily left. And I don't recall him ever returning.

Some come here wanting free engineering services. Simple circuits - that's easy enough. But when they want to know how to control something in a complex way but don't want to give away what they're doing with it, they're not going to get the kind of help they want.

Where I live, I've never seen, or even heard of a resistor built into a phone socket. That doesn't mean there isn't any, just something I needed greater clarification. Thanks Mr. Bill, for clarifying that. Now we have to assume the 470KΩ is no greater than a 20% accuracy. Unless someone knows better. I still don't think the TS has said what the precision level of the resistor is. I'll have to look back through the entire thread to see. I DO recall some saying what values they can expect at 20, 10, 5 and 1%. But I don't recall a specific answer to that question.
Follow the link in post #15, and in the section about sockets there is mention of a 470K resistor. Not a lot, but evidently it is there for some purpose.
So it is not somebody's million dollar idea just wanting a way to verify presence for some reason.
 

Tonyr1084

Joined Sep 24, 2015
5,039
OK, assuming I build this tester and my eight year old grandson is going to use it to test phone circuits:
A simple NO-GO / GO / NO-GO situation.
An open circuit - you get the first NO-GO indication.
A short circuit - you get the last NO-GO indication.
470KΩ you get the GO indication. How would I build that?

Since there are extremes between 470K and "Open" or "Short", I'm not going to worry about tolerances. I'd go with a window comparator. With an open circuit you get no lights. With a short you get a red light. With something above a short circuit you get a green light. If I want three lights, I'd include a power on light.

Will have to think about it a bit. But assuming the above, that's the route I'd investigate. Unless someone has a better idea. Maybe one light = OPEN, two lights = 470K, three lights = SHORT. That shouldn't be hard.
 

KMoffett

Joined Dec 19, 2007
2,902
With my micro controller circuit, or a window comparator, if your grandson gets a non-green LED indication, he says" "Gandpa, there is a problem with this one!" :)
 

Tonyr1084

Joined Sep 24, 2015
5,039
I'm having trouble figuring out a three light system (Green / Yellow / Red) (Where Green is good, Yellow is Open and Red is Short).
 

Thread Starter

ConnaTC

Joined Jun 20, 2020
18
Hi Guys sorry for the late reply, The capacitor in the socket is only used to ring the telephone with different voltage, a normal working voltage of a Phone line is 48v the resistor is used for bt’s line test system to check that there is a socket connected.

also thank you all for your feedback and opinions
 

MisterBill2

Joined Jan 23, 2018
6,997
Two comparators, and three resistors in a window comparator circuit. One red LED , anode to V+ through a resistor, the cathode tied to both comparator outputs tied together. The green LED anode connected from the same point to supply negative.
If the resistance is over or under then the red LED is on because one comparator pulls down, while if it is in the band then the Green LED is bright and the red ones are dim.
The three resistors biasing the inputs will take a bit of figuring.
 

KMoffett

Joined Dec 19, 2007
2,902
I'm having trouble figuring out a three light system (Green / Yellow / Red) (Where Green is good, Yellow is Open and Red is Short).
The LED colors are arbitrary. The three colors indicate that the line resistance is within spec, the line resistance in greater than spec ( high or open?), or the line resistance is less that spec (low or shorted ). Either with a window comparator or a micro-contoller. Is that clear?
 

Tonyr1084

Joined Sep 24, 2015
5,039
Like I said, I can't figure out how to get three states (three LED's). I can (and have) draw a two state tester. In the circuit below Open or Short you get a red light. Only when the resistance is between the upper and lower limits will you get a green light. And yes, you can use two 10KΩ pots for the limit controls.

I used a 9V battery and calculated for a current of 10 mA through each LED. Resistor values shown are exact requirements. Use of very close standard resistance will yield good results. Instead of the 700Ω resistor, a 680Ω will produce nearly the same results.
1592855493696.png
 

KMoffett

Joined Dec 19, 2007
2,902
Like I said, I can't figure out how to get three states (three LED's). I can (and have) draw a two state tester. In the circuit below Open or Short you get a red light. Only when the resistance is between the upper and lower limits will you get a green light. And yes, you can use two 10KΩ pots for the limit controls.

I used a 9V battery and calculated for a current of 10 mA through each LED. Resistor values shown are exact requirements. Use of very close standard resistance will yield good results. Instead of the 700Ω resistor, a 680Ω will produce nearly the same results.
View attachment 210488

Like this: 3-State LEDs window comparator
 

KMoffett

Joined Dec 19, 2007
2,902
I notice it requires two voltages; +15 and -15. Doable. Even if you go with two 9V batteries for portability sake. One thing you want is a push to test button. Otherwise one LED will always be on. Until the battery goes dead that is.
Sorry, I didn't flesh that circuit out for the OP's purpose. I left out the the internal 470K resistor, and the DPST push button switch that you push after you plug the black box in, and the the telephone plug, and the two trim pots and four resistors in place of the three series resistor voltage divider string so they can tweak the trip points.

It was a example of how a window comparator circuit could show three states with three LEDs to answer your not being to understand how a three state LED circuit could work...in Post#51.
 
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