CN104020332A - Multifunctional portable oscilloscope - Google Patents

Abstract

A multifunctional portable oscilloscope is composed of system hardware and system software. The multifunctional portable oscilloscope is characterized in that the system hardware comprises a signal input and attenuation circuit, a trigger circuit, an information acquisition and processing module (MCU module) and a liquid crystal module. A signal input module is arranged in the attenuation circuit. The attenuation circuit is connected with an ADC input pin of a single-chip microcomputer, an FSMC (variable static memory) and a TFT liquid crystal screen. The single-chip microcomputer is also connected with a touch screen on the TFT screen through an SPI bus. The MCU module is arranged in the single-chip microcomputer.

Description

Multifunctional portable oscillograph

Technical field

The present invention relates to field of embedded technology, relate in particular to the field of single-chip microcomputer.

Background technology

Oscillograph is a kind of purposes electronic measuring instrument very widely.It can become observable image invisible naked eyes converting electrical signal, is convenient to people and studies the change procedure of various electrical phenomenas.

Oscillograph can be divided into two classes at present: simulation class and numeric class.That simulation class oscillograph utilizes is narrow, by the molecular electron beam of High-speed Electric, beat on the panel that scribbles fluorescent material, just can produce tiny luminous point.Under the effect of measured signal, electron beam just looks like the nib of one-pen, can on panel, depict the change curve of the instantaneous value of measured signal.Numeric class oscillograph has utilized analog to digital converter (ADC) that continually varying voltage signal conversion is processed to microprocessor for digital data transmission.Make like this numeric class oscillograph there is more function than simulation class oscillograph.

Use oscillographic time signal frequency in majority circuit substantially below 1M, can directly use AD sampling in monolithic Bigpian to realize for such low frequency signal, do not need expensive high-speed ADC, simultaneously because the processing speed of single-chip microcomputer is not high, if so used high-speed ADC must reach and coordinate the AD sampling of ADC realization high speed and the storage of data with CPLD or the programmable logic gate chip of this class of FPGA so, so, use the oscillograph cost of high-speed ADC greatly to increase.So, develop a small-sized, low-power consumption, oscillograph becomes necessity cheaply.

Now on market, common traditional oscillograph volume is generally very large, and very heavy, and one hand is mentioned and all felt heavier, let alone has carried.Simultaneously common oscillograph price is all thousands of, and performance is high all up to ten thousand again, can significantly find out that prices are rather stiff.

Certainly, also there are some minoscilloscopes to be developed, such as the patent No. patent that is CN200420023369.6, although this oscillograph build is less, but must could normally work by USB and computing machine, the volume reducing by the method for sacrificing screen, does like this and can not meet portable demand.

Moreover, as this patent of CN200620017850.3, this is by each unit is bundled in to the volume reducing on oscillograph circuit board by mode stacked or tiling, but doing like this volume still can not reduce too much, because this works are with respect to the way of CN200620017850.3, the volume not reducing by changing the combination in space, but only complete sampling with single-chip microcomputer, storage, process, show this few sport work, need multiple modules jointly to complete these work with respect to other oscillographs, fundamentally reduce volume, also saved cost simultaneously.

Summary of the invention

Goal of the invention: solve existing instrument ordinary oscilloscope volume large, the shortcomings such as price, invented small-sized, at a low price and the portable only oscillograph taking single-chip microcomputer as core.

Technical scheme: a kind of multifunctional portable oscillograph, formed by system hardware and system software, system hardware comprises signal input and attenuator circuit, trigger circuit, information acquisition and processing module (MCU module) and Liquid Crystal Module, in attenuator circuit, be provided with signal input module, attenuator circuit is connected with the ADC input pin of single-chip microcomputer, be connected with TFT liquid crystal display with FSMC (variable static memory), single-chip microcomputer is also connected with the touch-screen on TFT screen by spi bus, is provided with MCU module in single-chip microcomputer.

Signal input comprises the input circuit of signal attenuation circuit, formed by resistance and electric capacity, and two electric capacity in parallel on the circuit of electric resistance partial pressure, capacitance ratio and the resistance ratio of electric capacity are inversely proportional to.

Attenuator circuit is carried out to impedance transformation, utilize voltage follower input resistance greatly and the little characteristic of output resistance, allow the ratio of attenuator satisfied 1/4 be transported to totalizer simultaneously.

Before the ADC of MCU sampled voltage, add a totalizer.

Trigger circuit are configured to and utilize voltage comparator, in the time that amplifier is operated in open loop mode, if the voltage that in-phase input end is IN1+ and IN2+ is the voltage of IN1-and IN2-higher than inverting input, amplifier output terminal is OUT1 and OUT2 meeting input high level, otherwise meeting output low level can be that RES_AJ regulates end of oppisite phase voltage to produce suitable trigger pulse by potentiometer like this.

Signals collecting and processing are sampled by ADC1 and two passages of ADC2 of MCU, and signals collecting adopts DMA transmission mode, and ADC1 has adopted the Channel0 of the Stream0 of DMA2, and ADC2 has adopted the Channel1 of the Stream2 of DMA2.

1: input signal is directly connected to attenuator circuit decays to original signal, carries out impedance transformation simultaneously.

2: the signal after processing is directly connected with the ADC input pin of single-chip microcomputer, for single-chip microcomputer sampling and processing.

3: single-chip microcomputer is connected with TFT liquid crystal display by FSMC (variable static memory), shows image with this.

4: single-chip microcomputer is also connected with the touch-screen on TFT screen by spi bus, the coordinate when obtaining user's touch-control to screen.

Beneficial effect: the present invention has used the high-performance microprocessor of stm32 to remove independent ADC chip with this, because high-speed ADC price is very expensive, but the range of signal of usually measuring is mostly below 1M, the advantage of independent high-speed ADC chip not obvious in this 1M low frequency signal once, so for this situation, these works have directly removed independent ADC chip, directly adopt the ADC of single-chip microcomputer inside to sample, so not only greatly reduce cost, also reduce volume, simplified circuit simultaneously.In addition, button and the knob of One's name is legion on traditional oscillograph saved in the operation of full touch-control, further reduced again volume.Like this, these works can do very littlely by volume, not only portable, and cost is also extremely cheap, reaches superelevation cost performance, can meet general demand.

Brief description of the drawings:

Fig. 1 signal attenuation circuit

Fig. 2 voltage follower

Fig. 3 totalizer

Fig. 4 voltage comparator (for generation of trigger pulse)

Each channel request in the DMA2 of Fig. 5 STM32F4

Fig. 6 process flow diagram

Embodiment

1: system overview:

System mainly comprises signal input and attenuator circuit, trigger circuit, MCU module and Liquid Crystal Module.For load module, adopt the mode of resistance and capacitance partial pressure to decay to input signal, then finally export the signal of 0--3V to the AD input end of MCU by a voltage follower and totalizer.

2: the Hardware Design:

2.1 signal inputs

2.1.1: signal attenuation:

Decay partial circuit as shown in Figure 1:

Can see, input circuit is made up of resistance and electric capacity, resistance has good attenuation to voltage in low frequency signal, the ratio of decay is 330/ (50+470+470+330)=1/4 simultaneously, it is original 1/4 that to be input circuit dropped to applied signal voltage amplitude, namely-1.5V--1.5V.In addition, electric capacity has good attenuation in high-frequency signal, because can there is distributed capacitance in the circuit after attenuator circuit, if do not adopt the mode of electric capacity in prime dividing potential drop, can cause high-frequency signal distortion.So, two electric capacity in same parallel connection on the circuit of electric resistance partial pressure, object is the impact in order to reduce subordinate's distributed capacitance, prevents waveform distortion.The capacitance ratio of electric capacity should be inversely proportional to resistance ratio simultaneously, so select the electric capacity of 10pf and 30pf to be connected in parallel on respectively resistance two ends at this.Because the AD input voltage range of MCU is 0--3V, so the amplitude of input signal can be-6V--6V.

2.1.2: impedance transformation and totalizer

Fig. 2 is voltage follower, its effect is that the signal after decay is carried out to impedance transformation, because there is the resistance of 400K between the signal input part of totalizer and 1.5V, if the signal after Fig. 1 decay is directly sent into totalizer, be equivalent to so the resistance of a 400K in parallel between the output terminal of Fig. 1 and 1.5V, so, the linear relationship of resistance and the electric capacity dividing potential drop to source signal is no longer just 1/4 of calculating before.But need to reach-6V--6V of the input voltage range of these works, so dividing potential drop ratio must strictly keep 1/4, so just be necessary attenuator circuit to carry out impedance transformation, utilize the large and little characteristic of output resistance of voltage follower input resistance, allow the ratio of attenuator satisfied 1/4 be transported to totalizer simultaneously.

Fig. 3 is totalizer, because the AD sampled voltage scope of MCU is 0--3V, so signal is added to 1.5V by totalizer, the signal source scope of-1.5V--1.5V can be transformed into 0--3V like this, samples for MCU.

Voltage comparator as shown in Figure 4, in the time that amplifier is operated in open loop mode, if the voltage of in-phase input end (IN1+ in figure and IN2+) is higher than the voltage of inverting input (IN1-in figure and IN2-), amplifier output terminal (OUT1 in figure and OUT2) meeting input high level, otherwise meeting output low level, can regulate end of oppisite phase voltage to produce suitable trigger pulse by potentiometer (RES_AJ in figure) like this, form trigger circuit.

2.2 trigger circuit:

The demonstration of the effect of trigger circuit in order to stablize waveform with this to trigger pulse of MCU.As Fig. 4: utilize LM339 as voltage comparator, with this, come on that input signal is converted into periodic square wave, and it is to close trigger or adopt rising edge to trigger and adopt negative edge to trigger 3 kinds of triggering modes that user can select.Program can, according to user's selection, operate accordingly in the time that trigger pip arrives.

2.3 signals collecting and processing:

This system is sampled by ADC1 and two passages of ADC2 of MCU.In order to reach maximum speed, when signals collecting, adopt the mode of DMA transmission.Direct memory access (DMA) (DMA) is used to provide in the high speed data transfer between peripheral hardware and storer or between storer and storer.Need not intervene by CPU, data can move rapidly by DMA, and this does other operations with regard to having saved the resource of CPU.

Fig. 5 is peripheral hardware corresponding to the every passage of the DMA2 in STM32F4 databook, can see, ADC1 correspondence the Channel0 of Stream0 and the Channel0 of Stream4, ADC2 correspondence the Channel1 of Stream2 and the Channel1 of Stream3.In native system, ADC1 has adopted the Channel0 of the Stream0 of DMA2, and ADC2 has adopted the Channel1 of the Stream2 of DMA2.

In internal memory, have the buffer of three 1024*2byte, wherein two are used for storing ADC1 and ADC2 sampled value, and another one is the AD value of the virtual waveform that after completing for store sample, waveform performed mathematical calculations.When user select time, stepping was less than 20us time, DMA can put into the data that collect in buffer.While being more than or equal to 50us, MCU will pass through the time stepping computation delay time, adopts a secondary data every a time delay, realizes the adjustable function of time gear with this.

After data acquisition completes, remaining part is drawn exactly, selects by user, also can carry out respective handling to waveform, such as drawing lissajous figures or carrying out Fast Fourier Transform (FFT) (FFT).Realize in the DSP storehouse that wherein FFT has adopted ST official to provide, and 1024 FFT only need several milliseconds, and slewing rate is very fast.

2.4 liquid crystal displays:

Display section has adopted the TFT screen of 400x240 resolution.STM32 drives liquid crystal with FSMC.Flexibly static memory controller (FSMC) can with synchronize or asynchronous memory and 16 PC memory card interface.As long as carry out suitable configuration, also can realize 8086 sequential of liquid crystal.After the FSMC using, liquid crystal is write to data convenient and quick just as writing internal memory, refreshing a screen only need to be less than 5ms, display waveform easily.

3: Design of System Software:

Software is realized man-machine interaction by graphic user interface (GUI), and whether the demonstration of GUI control knob and menu can detect touch-screen after the every conversion of AD once and be pressed, and can carry out corresponding operation if be pressed.Roughly flow process is as follows:

In program, have topmost global variable a: State, this is a structure variable, and structure is as follows:

Because buffer can store 1024 AD values in the inside, but screen level resolution only has 400, so be provided with the such variable of H_OffsetCHx and V_OffsetCHx, its effect is after sampling completes, the starting data address of the waveform of drawing on screen is that the base address of buffer adds the address after H_OffsetCHx, so, can be by the value of amendment OffsetCHx and V_OffsetCHx, just can whole 1024 points of display waveform, the phenomenon being reacted on TFT is: in the time that the value of ControlCH is corresponding passage, as long as finger slides on touch-screen, just can drag arbitrarily waveform, make to operate more vivid, observe also convenient.

Claims (7)

1. a multifunctional portable oscillograph, formed by system hardware and system software, it is characterized in that, system hardware comprises signal input and attenuator circuit, trigger circuit, information acquisition and processing module (MCU module) and Liquid Crystal Module, in attenuator circuit, be provided with signal input module, attenuator circuit is connected with the ADC input pin of single-chip microcomputer, be connected with TFT liquid crystal display with FSMC (variable static memory), single-chip microcomputer is also connected with the touch-screen on TFT screen by spi bus, is provided with MCU module in single-chip microcomputer.

2. multifunctional portable oscillograph according to claim 1, it is characterized in that: signal input comprises the input circuit of signal attenuation circuit, formed by resistance and electric capacity, two electric capacity in parallel on the circuit of electric resistance partial pressure, capacitance ratio and the resistance ratio of electric capacity are inversely proportional to.

3. multifunctional portable oscillograph according to claim 2, is characterized in that, attenuator circuit is carried out to impedance transformation, utilizes voltage follower input resistance greatly and the little characteristic of output resistance, allows the ratio of attenuator satisfied 1/4 be transported to totalizer simultaneously.

4. multifunctional portable oscillograph according to claim 2, is characterized in that, adds a totalizer before the ADC of MCU sampled voltage.

5. multifunctional portable oscillograph according to claim 1, it is characterized in that, trigger circuit are configured to and utilize voltage comparator, in the time that amplifier is operated in open loop mode, if the voltage that in-phase input end is IN1+ and IN2+ is the voltage of IN1-and IN2-higher than inverting input, amplifier output terminal is OUT1 and OUT2 meeting input high level, otherwise meeting output low level can be that RES_AJ regulates end of oppisite phase voltage to produce suitable trigger pulse by potentiometer like this.

6. multifunctional portable oscillograph according to claim 1, it is characterized in that, signals collecting and processing are sampled by ADC1 and two passages of ADC2 of MCU, signals collecting adopts DMA transmission mode, ADC1 has adopted the Channel0 of the Stream0 of DMA2, and ADC2 has adopted the Channel1 of the Stream2 of DMA2.

7. multifunctional portable oscillograph according to claim 1, is characterized in that, system software executive routine is as follows:

In program, have topmost global variable a: State, this is a structure variable, and structure is as follows: