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Old 13th October 2002, 03:29 AM   #1
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Default DIY curve tester

Does anyone know of a DIY tube curve tester ?
Something like Audiomatica's Sophia ?
Thanks.
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Old 14th October 2002, 01:28 PM   #2
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if you are going to DIY it, make sure to isolate the hot, HV end of things from the PC serial, parallel or USB interface -- many PCBoards (don't know if this is true in India) now have the parallel port on the mother board and inadvertent HV can fry the entire thing. (wasn't the case in the old 486 days!). <p>In all noisy, HV environments its a very good idea to separate your MCU from the analog input. You can consider using a voltage to frequency converter or an analog opto-isolator (like the Burr-Brown ISO amps or the Agilent HPCL-7850, or a dual diode device like the Agilent HCNR-200). <p> Of course, separate power supplies for the hot end and isolated ends, and separate grounds are necessary.
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Old 14th October 2002, 01:51 PM   #3
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Default Motherboards and HV

Hi Jackinnj,
The computer boards we have here are the same as the rest of the world. Most are from the Far East possibly even the Intel ones. All the ports are on board.
I think the best solution would be to do a V/F conversion and then couple with a simple opto coupler like a MCTXX or 4NXX series. The isolated side will run off low voltage rails. As you said the isolation from the HV side must be very good even at the power supply end.
Now what do I need to read these voltages ( or Freq ) into the computer. What kind of program should be written for this ?
I was wondering if the signals could be fed into a serial port and be read by some existing software and be reproduced as a graph ? Do I need to get something written in C++ ?
Thanks for your suggestions.
Cheers.
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Old 14th October 2002, 03:10 PM   #4
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If you condition the output of a VF converter a little bit you can measure the length of pulse or frequency with a PIC microcprocessor (or anyone elses MCU for that matter.) I use PIC's mostly, but do some stuff with AVR's. I guess it's because I started with the Basic Stamp about 5+ years ago and then moved on. <p> You can make a VF converter from a 555 or you can purchase a dedicated chip. The Nat Semi VF chip has excellent linearity. But for simplicity sake, and if you want to risk a 10-bit chip (they aren't that expensive anyway) just use a resistive divider and a microprocessor with built in-ADC, then isolate the output with 4N35's (of course, the serial port is going to look for something approximating RS232 levels and you have to trick it into doing this.)

You can use a program like Hyperterminal to talk to the microprocessor -- hyperterminal is on all machines using Microsoft. While it's not the best serial communications program (according to the serial guru's), it works fine for me.

I use a bunch of PIC's to talk to the serial port -- 16F84, 16F873, 16F877, 16C710 etc. Too lazy to program in assembly (most of the time) so I use PicBasic Pro. I also do some programming in VBasic -- you should plug into the microsoft public newsgroups for help in getting the DLL's you need to access hardware.
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