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Old Aug 25, 2004, 07:48 AM
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TAIWAN
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Digital Servo Tester / LCD Tachometer, Three in one V3.0

Digital Servo Tester / LCD Tachometer, two in one
http://www.geocities.com/ilufa/DST0.jpg

The digital servo tester have three test modes:

1. Manual mode

the PWM pulse width range from 1000uS~ 2000uS, 10uS/step with one touch neutral point (1500uS).

2 .Slow mode

take 18 second from 1000 to 2000 and reverse too, auto process 3 times

3. Fast mode

Jump between 1000 and 2000 every 0.3 second, auto process 5 times

 http://www.geocities.com/ilufa/DST_E.htm
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Last edited by ilufa; Sep 01, 2004 at 03:15 AM.
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Old Aug 26, 2004, 09:00 AM
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TAIWAN
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Version 2.0 available NOW!

with more test modes, include random test
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Old Aug 27, 2004, 04:50 AM
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Nice projects there, thanks for sharing.

Adam
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Old Aug 28, 2004, 10:32 PM
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TAIWAN
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schematic file DST.sch available
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Old Aug 31, 2004, 09:15 AM
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TAIWAN
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V 3.0

New function: receiver & transmitter test

also, speed controller test

V 3.0 Attention: one more resistor to protect the IC
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Old Jan 15, 2005, 10:02 AM
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TAIWAN
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V4.33 Multi tester for R/C

PIC16F88 with ADC
16x2 LCD with backlight, Mimic bar graphic
Analog knob input
Auto propeller air speed calculator
Bi-directional power protection
Voltmeter built-in


http://www.geocities.com/ilufa/MT/index_E.htm
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Old Jan 18, 2005, 09:07 AM
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Ilufa,

That is a pretty neat project you have there. I was thinking of doing something very similar to that myself. Of course, I was planning on using a Silicon Labs MCU. But that is purely academic. One thing I was thinking of adding that you don't seem to have yet. The ability to measure how much current the servo is drawing. One could put the servo into an oscillating pattern (back and forth) and then sample the current drawn by the servo. The data could be saved and sent to a PC via an RS232 port or USB port or the maximum simply displayed on the LCD display. One could also do this with a measured weight on the servo to measure the max current draw under loaded conditions. This could be very useful for determining how many servos can be used on a given BEC.

Just a thought.

Joe
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Old Jan 18, 2005, 07:17 PM
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TAIWAN
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Joe,

Certainly, this is a very good idea.

But PC programming is out of my ability. and for current measurement require addtonal Amp. circuit, make the DIY project more complicative.
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Old Jan 18, 2005, 08:49 PM
FDC
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Hi Ilufa,

I just noticed you're located in Taiwan. Well I'm currently on assignment in Taipei. Are the parts/components locally available in Taiwan particulary Taipei? Or dou you order them fro overseas also?

I'm keen on building one of your designs but I still don't know where the electronics part stores are located in Taipei. If you could give me some addresses of the electronics store in Taipei, I would highly appreciate it.

TIA!
FDC
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Old Jan 18, 2005, 11:20 PM
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TAIWAN
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Quote:
Originally Posted by FDC
Hi Ilufa,
If you could give me some addresses of the electronics store in Taipei, I would highly appreciate it.

TIA!
FDC
Located on Bade Road, Sec. 1, Guanghua Market is the largest market for electronics and computer products in Taiwan. Whatever you need in computer equipment, or the latest electronics, Guanghua Market has it all. Prices are low and often negotiable.

But PIC16F88 may not available, you can order it from microchip web
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Old Jan 19, 2005, 10:21 AM
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ilufa,
PC programming can be a bit daunting. But the circuit to read current may not need to be very complicated. Certainly no more complicated than the op-amps used in your tach circuit. In fact, a simple differential amplifier circuit would probably be all that is needed to amplify the signal. This would give you better resolution in the on board ADC. If you like, I could probably scratch together a drawing for you. It would be up to you to test it though. Work is too crazy right now for me to find the time.

Joe
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Old Jan 19, 2005, 08:24 PM
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Quote:
Originally Posted by jperch
ilufa,
If you like, I could probably scratch together a drawing for you. It would be up to you to test it though.
Joe
Joe,

Surely, If you draw, I will try to program it.

Ilufa
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Old Jan 20, 2005, 08:42 AM
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Ilufa,
Okay, give me some time. I will try to put a sketch together. What range does the ADC on your PIC controller measure?

Joe
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Old Jan 20, 2005, 05:08 PM
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Quote:
Originally Posted by jperch
Ilufa,
Okay, give me some time. I will try to put a sketch together. What range does the ADC on your PIC controller measure?

Joe
10 Bits ADC, ref.V = Vdd or Vss or Ext
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Old Jan 20, 2005, 05:50 PM
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Ilufa,
I hope this makes sense. Here is a PDF of what I drew. There is a connection labeled "To servo -". This means that instead of connecting the negative power lead of the servo to the tester's ground, you will connect it here instead. The output of the amplifier goes to the ADC input on the PIC. The value of R1 and R2 depend on the range of the ADC. If you are using VDD as the reference, then the range is 0 to VDD. I am assuming that is 3.3V. It also depends on how much current you expect to measure. With a 0.1 ohm resistor, a servo current of 5 amps would yield a 0.5V drop at the input of the amplifier. The gain would then need to be sufficient to amplify this to something close to the upper limit (3.3V). A gain of 6 would turn the 0.5V input into a 3.0V output. This would be very good. The equation for the gain of this amplifier is (1+R2/R1). So, if you needed a gain of 6, then R2 would need to be 5 times the value of R1. You could make R1 equal to 1k and R2 equal to 4.7k. This would give you a gain of 5.7 and you would be using resistor values that are typically available.

The op-amp is not really critical. You could probably use the LM358's that you have shown for the tach circuit. The best thing is to choose one that has a very low input current and a very small offset voltage. The other option is to calibrate out any error.

The idea of this circuit is that the current drawn by the servo will flow back through its negative lead. Since the op-amp has a very high input impedance virtually all of this current will flow through the 0.1 ohm resistor. This will create a voltage that is proportional to the current flow. You then use the amplifier to scale that voltage up to use as much of the range of the ADC as reasonable for best performance. Then you simply read the voltage with the PIC and then convert the reading into a current.

I hope you find this useful.

Joe
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