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This is a portable oscilloscope adapter that it can be held in breast pocket. Its operation is only sampling and sending to host PC. The most of functions of the oscilloscope are processed by host PC. Therefore, oscilloscope adapter can be simplified.
Specifications Acquisition 8bit, 10ksa/sec (fixed)
Input Voltage Ranges 1mV/lsb (256mVp-p/fs) Zi=1Mohm
3.3mV/lsb (853mVp-p/fs) Zi=1Mohm
10mV/lsb (2.56Vp-p/fs) Zi=10Mohm
30mV/lsb (8.53Vp-p/fs) Zi=10Mohm
100mV/lsb (25.6Vp-p/fs) Zi=10Mohm
300mV/lsb (85.3Vp-p/fs) Zi=10Mohm
Host Interface RS-232C (9pin)
Transmit: 115kbps, Receive: 9600bps
Between Internal circuit and Interface circuit
are isolated with optical-isolaters.
Storage and Display Host PC takes charge of all of them.
Power Requirement Battery: a 9V alkaline battery
Operating current: 15mA(10:1), 25mA(1:1)
No power switch. It is controlled by host PC via RS-232C.
Cost 3,000 Yens (parts)
Key Techniques
I saied that this is a simple A/D converter at top of this document. This means software quality affects to convenience to use.
But I think it has every advantage that most of processes are taken charge of by host PC. Sampling rate of 10ksa/sec is also slow for software processing, so that latest processors will be able to processes in real time with ease.
The sampling rate of 10ksa/sec is dissatisfied as a digital oscilloscple. This restriction on sampling rate is by be linked between acquisition unit and host PC with the RS-232C. However, it will be useful on the lower frequency signal.
Negative and positive powers for the analog circuit is generated with charge pump of the MAX232AC. The MAX232AC is useful when using OPAMP with single +5V power supply.
For range changing, this is controlled by host PC with atteneter and amplification value control commands. For others there is no especialy technique, only amplitude input signal, sampling with microcontroller with integrated ADC, and sending wave form data to host.
Control Program
This image of the wave form is displayed with sampling control program. It is a current waveform that acquired at the switch board with a current sensor.
Peaks that stand out from sine wave are input current of the PC that it has switching power supply. Sine wave is currernt of fluorescent lamps, refregerator and others. They are inductive load so that phase of their current is lagged. The functions of the control program are as follows.
•Vertical Scale: Input votage renge. When this item is changed, stops acquisition temporary and sends a command of range-change to the WCS and restart acquisition.
•Horizontal Scale: Sampling rate is fixed to 10ksa/sec so that changes the horizontal scale with compressing or expanding. 2.5ms is one horizontal dot par sample. For 50 and 250ms, they are displayed with untriggered roll.
•Trigger Mode: This is same function as other general oscilloscopes.
•Trigger Edge: This is same function as other general oscilloscopes.
•Trigger Level: This is same funciotn as other general oscilloscopes.
•Run/Stop: Acquisition Starts/Stops with space key.
•Working Envilonment: Control program runs on the real DOS or DOS window on the Windows9X. Serial port must be 16550A compatible (requires the FIFO).
When build it
This oscilloscope adapter using a TMP47P242VN 4bit microcontroller for acquisition control. But it is difficult to obtain and to programm personaly, so that I recommend to replace the microcontroller with any other microcontroller, such as PIC and AVR, when you want to follow this project. The details of the acquisition controller is as follows.
Communication format between host PC and oscilloscope adapter is N81 (no parity, 8 data bits, one stop bit). Data transfer rate between oscilloscope adapter and host PC is 115.2kbps. This is the minimun required transfer rate for real-time transmission of sampled data of 10ksa/sec. And command transfer speed of from host PC to oscilloscope adapter is 9.6kbps.
The acquisition controller will enter state of command waiting after power-up. One byte of command value range is from 0x50 to 0x5F, any other value will be ignored. The controller outputs lower four bits to P01-P03, wait for one milisecond, and enter to sampling state (sampling loop). In sampling state, anything data is raceived from host PC, acquisition controller will return to command waiting state. Host PC must send a 0x00 before sending any command.
When above protocol is satisfied, control program will be able to use without any patches. But remaking the controll program as windows based application will better than DOS based application.
(原文件名:wcs_inner.jpg)
(原文件名:wcs_scope.png)
(原文件名:wcs_sch.png) |
阿莫论坛20周年了！感谢大家的支持与爱护！！
月入3000的是反美的。收入3万是亲美的。收入30万是移民美国的。收入300万是取得绿卡后回国，教唆那些3000来反美的！
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发表于 2009-10-29 19:35:14
