Thanks for the reply Marty.
The original designer of course ran his ESR meter from four recharegable cells, which made little sense to me as they self discharge over time, and will probably be dead when I want to use the meter, apart from which, as the battery voltage diminished, it was necessary to have a front panel zero pot to enable the meter to read FSD for zero. On the other hand, a 9V PP3 battery is very cheap, has a shelf life of years, rather than Nicads/NIMH which discharge in weeks. (An earlier ESR meter I made from a design in the now defunct 'Television' magazine still has the same PP3 in it from eight years ago!). ESR meters are used only intermittently, and then only for a few minutes at a time, and so it seemed to me that it made more sense to fit a 78L05 regulator to provide a constant 5V from a 9V PP3. It also meant that the front panel pot could be replaced with a pre-set pot on the PCB to simplfiy construction and use, by minimising off-board wiring. Once set for FSD, the preset shouldn't need any further adjustment. (The original circuit didn't show the wiring of the front panel pot - it simply said: 'To 50uA meter and 25k zero pot', which many less experienced constructors found confusing, and wired up incorrectly).
When you say 'someone of my knowledge' I fear that you endow me with abilities that I'm afraid I don't possess, and in so doing, might give me delusions of adequacy! I don't see any sign of a C8 on the circuit or original PCB - I just left the 10uF cap C7 in place, popped a 78L05 100mA regulator in front of it, and amended the PCB track layout to accomodate it. It worked fine, still does, and I've had no feedback from anyone to suggest otherwise. However, I believe that it is customary when using voltage regulators to put a cap at the input to the regulator as well as on the output or there is a risk of self-oscillation. If that is so, what value do you suggest - another 10uF tantalum? As can be seen from the photo of the actual built PCB in my posting, there is space to add a couple of pads on the tracks for another cap adjacent to the 78L05.
I think the designer went through several iterations and on his final PCB layout the component numberings have several gaps in the numbering sequence for components that don't exist, either on the circuit or on the PCB.
I used a 100mA regulator for two reasons - firstly, the current drawn by the circuit is just a few mA - in fact the LED consumes more than does the instrument itself, so a 1A regulator wasn't called for, and secondly, it fitted on the PCB more easily than a 1A regulator.
I should once more, say that I claim no credit for the original concept and design, any such credit righlty beloniging to VE7IT, the originator. All I've done is to modify it to my own requriements, and to share my efforts with others, in the spirit of home-brew.
Once more Marty, thanks for your input.
David
The original designer of course ran his ESR meter from four recharegable cells, which made little sense to me as they self discharge over time, and will probably be dead when I want to use the meter, apart from which, as the battery voltage diminished, it was necessary to have a front panel zero pot to enable the meter to read FSD for zero. On the other hand, a 9V PP3 battery is very cheap, has a shelf life of years, rather than Nicads/NIMH which discharge in weeks. (An earlier ESR meter I made from a design in the now defunct 'Television' magazine still has the same PP3 in it from eight years ago!). ESR meters are used only intermittently, and then only for a few minutes at a time, and so it seemed to me that it made more sense to fit a 78L05 regulator to provide a constant 5V from a 9V PP3. It also meant that the front panel pot could be replaced with a pre-set pot on the PCB to simplfiy construction and use, by minimising off-board wiring. Once set for FSD, the preset shouldn't need any further adjustment. (The original circuit didn't show the wiring of the front panel pot - it simply said: 'To 50uA meter and 25k zero pot', which many less experienced constructors found confusing, and wired up incorrectly).
When you say 'someone of my knowledge' I fear that you endow me with abilities that I'm afraid I don't possess, and in so doing, might give me delusions of adequacy! I don't see any sign of a C8 on the circuit or original PCB - I just left the 10uF cap C7 in place, popped a 78L05 100mA regulator in front of it, and amended the PCB track layout to accomodate it. It worked fine, still does, and I've had no feedback from anyone to suggest otherwise. However, I believe that it is customary when using voltage regulators to put a cap at the input to the regulator as well as on the output or there is a risk of self-oscillation. If that is so, what value do you suggest - another 10uF tantalum? As can be seen from the photo of the actual built PCB in my posting, there is space to add a couple of pads on the tracks for another cap adjacent to the 78L05.
I think the designer went through several iterations and on his final PCB layout the component numberings have several gaps in the numbering sequence for components that don't exist, either on the circuit or on the PCB.
I used a 100mA regulator for two reasons - firstly, the current drawn by the circuit is just a few mA - in fact the LED consumes more than does the instrument itself, so a 1A regulator wasn't called for, and secondly, it fitted on the PCB more easily than a 1A regulator.
I should once more, say that I claim no credit for the original concept and design, any such credit righlty beloniging to VE7IT, the originator. All I've done is to modify it to my own requriements, and to share my efforts with others, in the spirit of home-brew.
Once more Marty, thanks for your input.
David
