Some of those meters come with a blue backlight 🙂Any screen will do, so long as it goes BLUE.
Yes, it's OK, I understand about the intended use of the LED.The color doesn't related to BLOD. It just shows a relative value of filament voltage.
I thought we were exchanging jokes about the type of indicators that give the best representation of the design philosophy of each other's power supply designs.... 🙂
The previous versions used to have a LCD, but I found that the communication between MCU and LCD is extremely noisy. Running SPI over FPC providing a display at the front is not a good choice in a tube amplifier.
My current design is a single RGB LED, using the gradient color from blue to green to yellow, then to red to show the relative voltage comparing with settings. The LED is placed on the board, with a optical conductive fibre connected to the front panel.
My thought is that such a meter circuit would normally be "out of the loop". It would have a rotary switch to select what tube, and a momentary push button that engages the meter readings of that tube (or parallel tube set) alone. Under normal amp use the meter is disconnected. It would have two LCD's one measures what the voltage the filament is currently settling at. The other would read the current through the tube. Then you just adjust the filament current trimmer to get the voltage correct and the fixed bias trimmer to re-bias the tube from time to time. So you don't need three hands I suppose the pushbutton could be a toggle switch, with a warning on the back to keep the meter turned off under normal use. Or you just keep the pushbutton and use a cheap Chinese 30 minute timer board to automatically turn off the meter.
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Yeah. What I want to provide with my module is that the power supply will do anything possible for users. It means that I'd like to make it ready for commercial applications.I thought we were exchanging jokes about the type of indicators that give the best representation of the design philosophy of each other's power supply designs.... 🙂
And I think you'd like to provide better sound performance while keep the design as simple as possible. Things lefted for users to do like calculating transformer voltage and adjusting current, is the cost of simple design.
That would be a system monitor for the whole amplifier. I've got some idea about this.My thought is that such a meter circuit would normally be "out of the loop". It would have a rotary switch to select what tube, and a momentary push button that engages the meter readings of that tube (or parallel tube set) alone. Under normal amp use the meter is disconnected. It would have two LCD's one measures what the voltage the filament is currently settling at. The other would read the current through the tube. Then you just adjust the filament current trimmer to get the voltage correct and the fixed bias trimmer to re-bias the tube from time to time. So you don't need three hands I suppose the pushbutton could be a toggle switch, with a warning on the back to keep the meter turned off under normal use. Or you just keep the pushbutton and use a cheap Chinese 30 minute timer board to automatically turn off the meter.
The monitor system is divided into one mother board and multiple signal isolator.
The mother board has ADC, MCU and LCD screen, and it can be switched off together with all signal isolator.
Each signal isolator has isolated amplifier and isolated power supply. It can sense differential voltage without a common ground, which can also be used for current sensing.
Signal isolators are set at every test point. The mother board collects data and show them on the screen. Rotary switch is not needed because adding channels is not so difficult. Showing all parameters at the same time is better for status checking.
How about a semi-automatic "diagnostic" device? Imagine a momentary push button on the back of the amp labeled "Run Diagnostics". When pressed it invokes a relay that applies mains power to the computer (probably a small SMPS). When the computer boots, it immediately runs the diagnostic program. This program reads all the analog and digital ports you've wired out to sensors in the circuit. What the voltage filaments are setting at, what the tube currents are, even on/off digital ports, are there speakers connected to the banana jacks? whatever needs to be made foolproof. The program checks to see that every voltage/current is still "in spec" (within a tolerance leeway 2%, 5% whatever). If everything is ok then the it writes "ALL GOOD" to the LCD panel and the computer sends a trigger to the AC relay to cut its power. But if the diagnostic program, lets say finds that V1's filament voltage is now settling at too high of a voltage, and V2 tube has gone cold is not passing enough current. It would write to the LCD "V1 FIL V HIGH" and "V2 CURRENT TOO LOW". In this case the program will keep the computer up. Now all the user needs to know is how to use a small screwdriver, no need for them to probe around with a DMM. They simply trim the Coleman filament trimmer of V1 until the error goes away. And they trim the bias of V2 until that error goes away. Now that the amp is back "in spec" the computer will display "ALL GOOD" and shut itself down. So the circuit has no noisy computer and SMPS in the chassis running. The amp is never "dependent" on a computer to operate the trimming. All sensors are powered down. Only the sense resistors remain in the circuit, those are transparent. The owner doesn't need to know anything about electronics except what trimmer to adjust, and point the trimmers to chassis holes to make it even easier, no need to open the enclosure. The computer gives a real-time feedback measurement loop. The computer kills itself whenever there is no diagnostic issue. After the adjustments, if the owner pressed the "RUN DIAGNOSTIC" button again, it would simply report "ALL GOOD" then shut down the computers SMPS right at the mains. Now you have an amp that is non-dependent upon the computer bricking, but you also have a "smart" built-in computer and diagnostic program available any time you need it at the push of a button. The Arduino has many analog and digital ports, lots of things in the amp can be verified in the software.
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I know what you mean.How about a semi-automatic "diagnostic" device?
But everyone's amplifier has different points to measure, and different reference value. It means that the program should be highly customized.
Comparing with saying "All Good", I prefer to show all parameters, and change the color of each parameter comparing to its standard value. It will greatly reduce the complexity of the code. Submenu or error summary is a waste of resources except when there're so many parameters that the screen can't show them all at the same time.
For example you see "V_FIL1: 5.54V" in red color in a 300B amplifier, then you know it's time to adjust the filament current of the corresponding tube. Adjust it until you see "V_FIL1: 5.05V" will be fine.
Or you see "I_k2: 30mA" in blue color in the same amplifier, then you know you should adjust bias for it, or replace the aged tube to see "I_k2: 70mA".
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