Thanks for your interest Phil.
Based of feedback and suggestions from others, I’ve extensively modified and updated the original design over time, and as a result, there have been so many posts to this thread that it’s all become rather confusing for anyone who wishes to build one! Also, as this is a relaxed forum with a ‘light touch’ moderation policy, (a big plus point IMHO), we do tend to drift off topic somewhat, so not all the posts are relevant or helpful to new readers.
If you wish to have a go at building the project, Posts # 1, 2 & 3 in this thread are relevant. Post 4 describes building and troubleshooting, and Post #40 shows pics of the latest PCB artwork and component layout. However, a number of builders have found the circuit a bit confusing as it didn't show how to wire the meter and off-board zero adjustment pot. Neither did it incorporate the additions that I’ve made over time, albeit I did update the PCB artwork and overlay. To help you or any other potential builders, your post has prompted me to update the circuit layout, incorporating all the additions that I’ve made, so I’ve done that today and have attached it to this post.
The original designer's article is here:
http://www.members.shaw.ca/swstuff/esrmeter.html
The Schematic is here:
http://www.members.shaw.ca/swstuff/esrschematic.png
The Original Parts Layout is here:
http://www.members.shaw.ca/swstuff/esrbuildit.png
Original x-ray of parts placement is here:
http://www.members.shaw.ca/swstuff/esrxray.png
Those should be viewed alongside my updated layout and parts placement, showing the changes to the layout. Most parts placements are the same, but where I’ve added components and altered the layout, I’ve highlighted those on the PCB overlay.
I hope that’s helpful to you or anyone else wishing to build the project. Many have successfully been built, and if anyone gets stuck, I’m happy to help as best I can. It isn't a temperamental circuit, the parasts are widely avaiable and cheap - even the meter movement isn't too expensive, and once built, it's a very useful item of test gear.
A quick explanation once more as to how it works and what the various bits of the circuit do:
IC1 is a hex Schmidt trigger. One of the six gates, along with C1 and R1, form an oscillator circuit, which is as simple as an oscillator gets. The values of C and R determine the oscillator frequency, which the designer states as 150 or 156kHz, but is in fact nearer to 100KHZ, though this isn’t critical and has no bearing on the accuracy of the meter. Most ESR meters work on a similar principle - the application of a low amplitude AC signal, usually of a frequency between 100kHz - 200kHz, to the capacitor under test. I’ve tried various 74HC14N ICs in this design and they’ve ranged from 100 – 105 kHz. More about that in the footnote. . (The ‘N’ suffix simply denotes a 14 pin DIL package. Any prefix denotes the ID of the maker)
Pin 2 of IC is the output of the oscillator, which goes to the input of the other gates at pins 3,5,9,11 & 13. The outputs of those five gates appear at pins 4,6,8,10 & 12 and go to the five 680 Ohm resistors R2,3,4,5 & 6, to form a buffer and Low Pass filter. At the junction of those resistors - which are all coupled together on their outputs - there should be a waveform of approximately 250mv peak to peak at about 100KHz. The next stage is the input protection stage (D5, D6, C5 etc) which protects the meter from damage should it get zapped with an un-discharged capacitor attached to the test leads.
From the junction of R8, D5, D6 and C5, there should be a waveform of about 180mV peak to peak, but it’s important to note that this is only when the test leads are shorted, or a good cap with a low ESR is connected to them. This AC waveform then passes via C2 to the base of the 2N2222A which is an AC amplifier with a gain of approx 10.5. Its role in life is to raise the 180mV p-p input to nearer 2 Volts p-p. This then passes to the meter rectifier D1,2,3 &4, for the meter movement. But without the test leads shorted, or a known good electrolytic cap with a low ESR attached to the test leads, there will be zero Volts at the input (base) of the 2N2222A and nothing at its output, (collector) so no deflection on the meter. The meter rectifier enables the meter to function as an expanded scale AC voltmeter. Full scale is zero Ohms, mid-scale is approx 10 Ohms. There is no DC output until approx 75 Ohms of ESR is seen at the test terminals, (ie, a bad cap), at which point the meter will barely deflect.
The meter reads like an analogue Ohmmeter, that is when you short the test leads, the needle deflects across tot the right hand end of the scale. But whereas on an Ohmmeter you have to set the zero each time you use it, because this project incorporates a 5V regulator and is powered from a 9V battery, once you’ve set the on-board pre-set pot to enable the meter to read full scale deflection, it shouldn’t be necessary to adjust it again. If the needle doesn’t go to FSD with the test leads shorted, it is a sign that the battery Voltage has fallen below 5 Volts and needs replacing
As I explained in an earlier post, while I originally used a 50 uA meter from the aptly named ESR Electronics, I later found that Rapid Electronics supply a larger 50uA meter (70mm x 60mm):
http://www.rapidonline.com/Electrical-Po...70-48-0300
Hope that helps.
Based of feedback and suggestions from others, I’ve extensively modified and updated the original design over time, and as a result, there have been so many posts to this thread that it’s all become rather confusing for anyone who wishes to build one! Also, as this is a relaxed forum with a ‘light touch’ moderation policy, (a big plus point IMHO), we do tend to drift off topic somewhat, so not all the posts are relevant or helpful to new readers.
If you wish to have a go at building the project, Posts # 1, 2 & 3 in this thread are relevant. Post 4 describes building and troubleshooting, and Post #40 shows pics of the latest PCB artwork and component layout. However, a number of builders have found the circuit a bit confusing as it didn't show how to wire the meter and off-board zero adjustment pot. Neither did it incorporate the additions that I’ve made over time, albeit I did update the PCB artwork and overlay. To help you or any other potential builders, your post has prompted me to update the circuit layout, incorporating all the additions that I’ve made, so I’ve done that today and have attached it to this post.
The original designer's article is here:
http://www.members.shaw.ca/swstuff/esrmeter.html
The Schematic is here:
http://www.members.shaw.ca/swstuff/esrschematic.png
The Original Parts Layout is here:
http://www.members.shaw.ca/swstuff/esrbuildit.png
Original x-ray of parts placement is here:
http://www.members.shaw.ca/swstuff/esrxray.png
Those should be viewed alongside my updated layout and parts placement, showing the changes to the layout. Most parts placements are the same, but where I’ve added components and altered the layout, I’ve highlighted those on the PCB overlay.
I hope that’s helpful to you or anyone else wishing to build the project. Many have successfully been built, and if anyone gets stuck, I’m happy to help as best I can. It isn't a temperamental circuit, the parasts are widely avaiable and cheap - even the meter movement isn't too expensive, and once built, it's a very useful item of test gear.
A quick explanation once more as to how it works and what the various bits of the circuit do:
IC1 is a hex Schmidt trigger. One of the six gates, along with C1 and R1, form an oscillator circuit, which is as simple as an oscillator gets. The values of C and R determine the oscillator frequency, which the designer states as 150 or 156kHz, but is in fact nearer to 100KHZ, though this isn’t critical and has no bearing on the accuracy of the meter. Most ESR meters work on a similar principle - the application of a low amplitude AC signal, usually of a frequency between 100kHz - 200kHz, to the capacitor under test. I’ve tried various 74HC14N ICs in this design and they’ve ranged from 100 – 105 kHz. More about that in the footnote. . (The ‘N’ suffix simply denotes a 14 pin DIL package. Any prefix denotes the ID of the maker)
Pin 2 of IC is the output of the oscillator, which goes to the input of the other gates at pins 3,5,9,11 & 13. The outputs of those five gates appear at pins 4,6,8,10 & 12 and go to the five 680 Ohm resistors R2,3,4,5 & 6, to form a buffer and Low Pass filter. At the junction of those resistors - which are all coupled together on their outputs - there should be a waveform of approximately 250mv peak to peak at about 100KHz. The next stage is the input protection stage (D5, D6, C5 etc) which protects the meter from damage should it get zapped with an un-discharged capacitor attached to the test leads.
From the junction of R8, D5, D6 and C5, there should be a waveform of about 180mV peak to peak, but it’s important to note that this is only when the test leads are shorted, or a good cap with a low ESR is connected to them. This AC waveform then passes via C2 to the base of the 2N2222A which is an AC amplifier with a gain of approx 10.5. Its role in life is to raise the 180mV p-p input to nearer 2 Volts p-p. This then passes to the meter rectifier D1,2,3 &4, for the meter movement. But without the test leads shorted, or a known good electrolytic cap with a low ESR attached to the test leads, there will be zero Volts at the input (base) of the 2N2222A and nothing at its output, (collector) so no deflection on the meter. The meter rectifier enables the meter to function as an expanded scale AC voltmeter. Full scale is zero Ohms, mid-scale is approx 10 Ohms. There is no DC output until approx 75 Ohms of ESR is seen at the test terminals, (ie, a bad cap), at which point the meter will barely deflect.
The meter reads like an analogue Ohmmeter, that is when you short the test leads, the needle deflects across tot the right hand end of the scale. But whereas on an Ohmmeter you have to set the zero each time you use it, because this project incorporates a 5V regulator and is powered from a 9V battery, once you’ve set the on-board pre-set pot to enable the meter to read full scale deflection, it shouldn’t be necessary to adjust it again. If the needle doesn’t go to FSD with the test leads shorted, it is a sign that the battery Voltage has fallen below 5 Volts and needs replacing
As I explained in an earlier post, while I originally used a 50 uA meter from the aptly named ESR Electronics, I later found that Rapid Electronics supply a larger 50uA meter (70mm x 60mm):
http://www.rapidonline.com/Electrical-Po...70-48-0300
Hope that helps.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
