CN118944667A - Low-frequency analog quantity sampling circuit and acquisition method based on resistance sensor - Google Patents
Low-frequency analog quantity sampling circuit and acquisition method based on resistance sensor Download PDFInfo
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- CN118944667A CN118944667A CN202411423825.4A CN202411423825A CN118944667A CN 118944667 A CN118944667 A CN 118944667A CN 202411423825 A CN202411423825 A CN 202411423825A CN 118944667 A CN118944667 A CN 118944667A
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- 238000000034 method Methods 0.000 title claims abstract description 16
- 239000003990 capacitor Substances 0.000 claims abstract description 104
- 238000007599 discharging Methods 0.000 claims description 8
- 238000013139 quantization Methods 0.000 abstract description 9
- 238000006243 chemical reaction Methods 0.000 description 10
- 238000010586 diagram Methods 0.000 description 4
- 230000008878 coupling Effects 0.000 description 3
- 238000010168 coupling process Methods 0.000 description 3
- 238000005859 coupling reaction Methods 0.000 description 3
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/12—Analogue/digital converters
- H03M1/124—Sampling or signal conditioning arrangements specially adapted for A/D converters
- H03M1/1245—Details of sampling arrangements or methods
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Abstract
The invention relates to a low-frequency analog quantity sampling circuit based on a resistance type sensor and a collection method thereof, and the low-frequency analog quantity sampling circuit comprises a sampling resistor, a fixed capacitor, a reference voltage, a voltage comparator and an MCU (micro control unit), wherein one end of the sampling resistor is connected with a constant voltage source, the other end of the sampling resistor is connected with the fixed capacitor, the sampling resistor and the fixed capacitor are connected in series to form an RC (resistor-capacitor) charging circuit, one end of the fixed capacitor is grounded, the non-grounded end of the fixed capacitor is coupled with an I/01 port of the MCU, one end of the fixed capacitor, which is coupled with the MCU, is coupled with one input end of the voltage comparator, the reference voltage is connected with the other input end of the voltage comparator, the output end of the voltage comparator is connected with the I/02 port of the MCU, and a timer is configured in the MCU. The circuit obtains the digital quantity of the analog quantity signal quantized in time, has simple structure and lower cost, can be expanded into multi-channel simultaneous acquisition, and can obtain high quantization resolution when being suitable for a common low-price MCU.
Description
Technical Field
The invention relates to the field of sensors, in particular to a low-frequency analog quantity sampling circuit based on a resistance type sensor and a sampling method thereof.
Background
The resistive sensor detects a certain characteristic or state to be measured by measuring a change in resistance value, and generally, analog quantity is collected by converting the analog quantity into voltage, and then the voltage is quantized by an AD conversion circuit and then converted into digital quantity. The quantization resolution is related to the AD conversion circuit, and the higher the quantization resolution is, the higher the conversion cost is. For the low-frequency analog signal, if the analog quantity is converted into the charging time of the capacitor, the digital magnitude of the analog signal can be obtained without an AD conversion circuit, and the quantized resolution can be greatly improved.
Disclosure of Invention
In view of the shortcomings of the background art, the invention aims to provide a low-frequency analog quantity sampling circuit based on a resistance type sensor, which is used for obtaining the digital quantity of an analog quantity signal quantized in time.
The invention is completed by adopting the following technical scheme: the utility model provides a low frequency analog quantity sampling circuit based on resistance type sensor, includes sampling resistor, fixed capacitor, reference voltage, voltage comparator and MCU, a constant voltage source is connected to sampling resistor one end, and the sampling resistor other end is connected with fixed capacitor, and sampling resistor and fixed capacitor establish ties into RC charging circuit, and fixed capacitor's one end ground connection, fixed capacitor non-ground end coupling are in MCU's I/01 port, and fixed capacitor and MCU coupling's one end coupling are in voltage comparator one input, reference voltage is connected with voltage comparator another input, voltage comparator output is connected with MCU's I/02 port, be provided with the timer in the MCU.
The method for collecting the low-frequency analog quantity sampling circuit based on the resistance type sensor comprises the following steps of,
Step1, rapidly discharging a fixed capacitor, wherein the rapid discharging time is t 1, so that the voltage drop at two ends of the capacitor is V 0;
Step 2, a constant voltage source charges a fixed capacitor through a sampling resistor, a timer of an MCU starts to count time, voltage at two ends of the capacitor rises, the voltage of the capacitor is transmitted to the voltage comparator through an input end of the voltage comparator, the voltage comparator compares the voltage of the capacitor with a reference voltage V 1, when the voltage of the capacitor exceeds the reference voltage V 1, the potential of an output end of the voltage comparator is turned over, the MCU generates interruption, the timer stops to count time, a first sampling time t is obtained, and a sampling time value t is in direct proportion to an analog sampling resistance value;
Step 3, after time delay t 2, repeating the step 1 to rapidly discharge the fixed capacitor, and repeating the step 2 to acquire the next sampling time value t;
And 4, acquiring capacitor charging time according to a certain sampling time interval, acquiring a sampling time value acquired at intervals, and acquiring the digital quantity of the analog quantity signal quantized in time based on the fact that the sampling time value is in direct proportion to the resistor.
Further, in step1, the step of rapidly discharging the fixed capacitor includes that the MCU sets the I/01 port to a quasi-bidirectional mode, pulls down the I/01 port, the fixed capacitor is in a short circuit state to ground, the fixed capacitor is rapidly discharged, after a delay time t 1, the voltage drop at two ends of the capacitor is 0 v, and the discharge of the fixed capacitor is completed.
Further, the sampling time interval should be greater than the charging time required by the RC charging circuit to charge from 0 volts to V 1, and the reference voltage V 1 should be less than the voltage V 2 of the constant voltage source.
The invention has the beneficial effects that:
1. The charging time of the fixed capacitor is monitored through the timer interval in the MCU, and according to the change of the charging time, the change of the analog quantity is represented in time quantization without conversion by an AD conversion circuit. The change of the measured analog quantity is converted into the change of resistance, and further converted into the change of the charging time of the fixed capacitor.
2. The circuit and the acquisition method are used for the MCU with common low price, the MCU with common low price can only be configured with an AD conversion circuit with resolution of only 8 bits or 10 bits, but can be configured with a 16-bit timer, so that the quantization index with 16-bit resolution can be obtained, and the high quantization resolution can be obtained.
3. The sampling circuit has a simple structure and low cost, can be expanded into multi-channel simultaneous acquisition, and makes up the situation that the built-in ADC port of the MCU is not enough in part of application occasions.
Drawings
FIG. 1 is a schematic diagram of a first embodiment of a low frequency analog sampling circuit based on a resistive sensor;
FIG. 2 is a schematic diagram of a voltage analog sampling circuit based on a resistive sensor;
FIG. 3 is a schematic diagram of a second embodiment of a low frequency analog sampling circuit based on a resistive sensor;
fig. 4 is a schematic diagram of a third embodiment of a low frequency analog sampling circuit based on a resistive sensor.
Detailed Description
In order to further describe the technical means and effects adopted by the present invention for achieving the intended purpose, the following detailed description will refer to the specific implementation, structure, characteristics and effects according to the present invention with reference to the accompanying drawings and preferred embodiments.
Referring to fig. 1-2, a first embodiment of the present invention provides a low-frequency analog sampling circuit based on a resistive sensor, which includes a sampling resistor 1, a fixed capacitor 2, a reference voltage 3, a voltage comparator 4 and an MCU5. One end of the sampling resistor is connected with a constant voltage source 6, the other end of the sampling resistor is connected with the fixed capacitor, and the sampling resistor and the fixed capacitor are connected in series to form an RC charging circuit. One end of the fixed capacitor is grounded, one end of the fixed capacitor, which is not grounded, is coupled to the I/01 port of the MCU, one end of the fixed capacitor, which is coupled to the MCU, is coupled to one input end of the voltage comparator, the reference voltage is connected with the other input end of the voltage comparator, the output end of the voltage comparator is connected with the I/02 port of the MCU, and a timer is configured in the MCU. Specifically, the input end of the voltage comparator comprises a non-inverting input end and an inverting input end, when one end of the fixed capacitor coupled with the MCU is coupled with the non-inverting input end of the voltage comparator, the reference voltage is connected with the inverting input end of the voltage comparator, and vice versa. The sampling circuit is suitable for analog quantities such as temperature, light intensity, weight or pressure, and the like, and is also suitable for voltage analog quantities.
When the analog quantity such as temperature, light intensity, weight or pressure is changed, the analog quantity is proportional to the change of resistance, which is proportional to the change of charging time of the capacitor, and thus the change of the analog quantity is proportional to the change of charging time. By collecting the time required by the capacitor to charge to a certain fixed voltage value, the analog quantity taking the time as a reference is obtained, and the change of the measured analog quantity is converted into the change of the resistance and further converted into the change of the charging time of the fixed capacitor without conversion by an AD conversion circuit.
Specifically, let V 0 be the initial voltage on the capacitor, V 2 be the voltage to which the capacitor is eventually charged, i.e. the voltage of the constant voltage source, and V t be the voltage value at time t
Since V t=V0+（V2-V0) [1-EXP (-t/RC) ]
So t=r×c×ln [ (V 2-V0)/(V2-Vt) ]
When charging to the reference voltage V 1, i.e. V t=V1, t=r×c×ln [ (V 2-V0)/(V2-V1) ]
Can be simplified to t=r×k, where k=c×ln [ (V 2-V0)/(V2-V1) ]
When V 0=0,V1,V2 takes a fixed value, K is a constant, so time t is proportional to R.
In particular, the analog quantities of pressure, weight, temperature, light intensity, etc., are proportional to the resistance in a certain range. These analog quantities are therefore proportional to time and can be formulated as y=k (t-t 0)+y0. Y is the measured value, y 0 is the analog quantity when the charging time is t 0. K is the scaling factor.
Specifically, taking weight as an example, when the weight is 0 (only tare weight), the charging time t 0 is measured, when the weight is 1 kg, the charging time t 1 is measured, then
K= (1-0)/(t 1-t0) when a certain weight y is measured for a time t, the weight y= (t-t 0)/(t1-t0) can be obtained
The method and sampling circuit are also applicable to voltage analog quantities, and the values of the resistor R and the capacitor C are fixed as shown in fig. 2. When there is no signal, the time t of collection is also fixed, when the signal voltage is positive, the time t of collection will become smaller, and when the signal voltage is negative, the time t of collection will become larger. From this, it can be seen that the time difference is still proportional to the input signal quantity, and an analog quantity based on the time amount is obtained.
The method for collecting the low-frequency analog quantity sampling circuit based on the resistance type sensor comprises the following steps:
And step 1, rapidly discharging the fixed capacitor, wherein the rapid discharging time is t 1, when the discharging of the fixed capacitor is completed, the voltage drop at the two ends of the capacitor is 0, and starting a timer of the MCU to count.
Specifically, in order to enable the capacitor to be charged and discharged orderly, the step of rapidly discharging the fixed capacitor comprises the steps that the MCU firstly sets the I/01 port to be in a quasi-bidirectional mode, and pulls down the I/01 port, and the fixed capacitor is in a short circuit state to the ground. The fixed capacitor discharges rapidly, the voltage drop at two ends of the capacitor is 0 after the delay time t 1, the discharge of the fixed capacitor is completed, the MCU sets the I/01 port to be in a leakage-opening mode, and the fixed capacitor is in an open circuit state to the ground.
And step 2, the constant voltage source charges the fixed capacitor through the sampling resistor, the voltage at two ends of the capacitor is increased, the capacitor voltage is transmitted to the voltage comparator through an input end of the voltage comparator, and the voltage comparator compares the capacitor voltage with the reference voltage. When the capacitor voltage exceeds the reference voltage, the potential of the output end of the voltage comparator is turned over, the MCU generates interruption, the timer is stopped to count, and the first sampling time t is obtained. The sampling time value t is in direct proportion to the analog sampling resistance value;
The specific fixed capacitor charging step comprises the following steps: the MCU sets the I/01 port to be in an open-drain mode, and the fixed capacitor is in an open-circuit state to the ground. The constant voltage source charges the fixed capacitor through the sampling resistor, and the MCU starts a timer to start timing. When the charging voltage exceeds the reference voltage V 1, the comparator output is turned over, the MCU generates an interrupt, and the timer is stopped to count, so that the charging time t is obtained.
And 3, after the time delay t 2, repeating the step 1 to rapidly discharge the fixed capacitor, and repeating the step 2 to acquire the next sampling time value t. I.e. the adjacent sampling time interval is t 1+t+t2, the sampling time interval is greater than the charging time of the RC charging circuit.
And 4, repeating the steps according to a certain sampling time interval to circularly acquire the capacitor charging time and acquire the sampling time value acquired at intervals. Based on the sampling time value being proportional to the resistance, a digital quantity of the analog quantity signal quantized in time is obtained.
The circuit and the acquisition method can be suitable for an MCU with a common low price, the MCU with the common low price can only be configured with an AD conversion circuit with the resolution of only 8 bits or 10 bits, but can be configured with a 16-bit timer, so that a quantization index with the resolution of 16 bits can be obtained, and a high quantization resolution is obtained. The problem of lower quantization resolution of the MCU with common low price is solved, and the cost is lower. Meanwhile, the sampling circuit is simple in structure, can be expanded into multipath simultaneous acquisition, and can make up for the condition that an MCU built-in ADC port is not enough in partial application occasions.
Examples
If the resistor R is a resistance strain gauge, the resistance value is 350 ohms. The reference voltage of the inverting input terminal of the comparator is 1.0V, the capacitance value C is 1uF, the constant voltage source is 3.3V, and the time required for charging the capacitor from 0V to 1.0V is 126 microseconds. When the stress increases, the resistance is greater than 350 ohms and the charge time is greater than 126 microseconds. The increased stress is proportional to the increased time. The sampling resistor of this embodiment is 350 ohms and the capacitance is 1uF, but other embodiments are not limited to this value.
Referring to fig. 3, a second embodiment of the present invention provides a low-frequency analog sampling circuit based on a resistive sensor, which includes a sampling resistor, a fixed capacitor and an MCU, and a timer is set in the MCU. One end of the sampling resistor is connected with a constant voltage source, the other end of the sampling resistor is connected with the fixed capacitor, the sampling resistor and the fixed capacitor are connected in series to form an RC charging circuit, the MCU is provided with an I/01 port input port, and the non-grounding end of the fixed capacitor is connected with the I/01 port.
The step of collecting the charging time of the fixed capacitor comprises the following steps: 1) The I/01 port of the MCU is firstly set to be in a quasi-bidirectional mode, and the I/01 port is pulled down; 2) The capacitor discharges rapidly, and after a short time t 1 (discharge time t 1), the voltage drop at two ends is 0; 3) The I/01 port is set to be in a high-impedance input mode, and the MCU starts a timer to start timing; 4) The constant voltage source charges the capacitor through the sampling resistor, and the voltage at two ends of the capacitor is increased; 5) The MCU repeatedly reads the value of the I/01 port, when the capacitor voltage exceeds a certain voltage, the MCU reads the value from 0 to 1, the timer is stopped to count, and the time t is proportional to the sampling resistance value.
Referring to fig. 4, a third embodiment of the present invention provides a low-frequency analog sampling circuit based on a resistive sensor, which includes a sampling resistor, a fixed capacitor, a switching triode, a voltage comparator and an MCU, wherein a timer is set in the MCU. The base electrode of the switching triode is connected with the I/01 port of the MCU through a resistor. In this embodiment, when a high potential is output through the I/01 port, the switching transistor 8 is turned on, the fixed capacitor 2 is in a short circuit state with respect to the ground, and the capacitor 2 is rapidly discharged. When the I/01 port outputs low potential, the switching triode 8 is cut off, the fixed capacitor is in an open circuit state to the ground, and the constant voltage source 6 charges the capacitor 2 through the resistor 1. The other steps are the same as in the first embodiment.
The present invention is not limited in any way by the above-described preferred embodiments, but is not limited to the above-described preferred embodiments, and any person skilled in the art will appreciate that the present invention can be embodied in the form of a program for carrying out the method of the present invention, while the above disclosure is directed to equivalent embodiments capable of being modified or altered in some ways, it is apparent that any modifications, equivalent variations and alterations made to the above embodiments according to the technical principles of the present invention fall within the scope of the present invention.
Claims (6)
1. A low-frequency analog sampling circuit based on a resistance type sensor is characterized in that: the constant-voltage circuit comprises a sampling resistor, a fixed capacitor, a reference voltage, a voltage comparator and an MCU, wherein one end of the sampling resistor is connected with a constant-voltage source, the other end of the sampling resistor is connected with the fixed capacitor, the sampling resistor and the fixed capacitor are connected in series to form an RC charging circuit, one end of the fixed capacitor is grounded, the non-grounded end of the fixed capacitor is coupled with an I/01 port of the MCU, one end of the fixed capacitor, which is coupled with the MCU, is coupled with one input end of the voltage comparator, the reference voltage is connected with the other input end of the voltage comparator, the output end of the voltage comparator is connected with the I/02 port of the MCU, and a timer is configured in the MCU.
2. The method for collecting the low-frequency analog quantity sampling circuit based on the resistive sensor according to claim 1, wherein the method comprises the following steps: the steps are as follows,
Step 1, a fixed capacitor is rapidly discharged, the rapid discharge time is t 1, the voltage drop at two ends of the capacitor is V 0, and a timer of an MCU is started to start timing;
Step 2, a constant voltage source with the voltage of V 2 charges a fixed capacitor through a sampling resistor, the voltage at two ends of the capacitor rises, the voltage of the capacitor is transmitted to a voltage comparator through an input end of the voltage comparator, the voltage comparator compares the voltage of the capacitor with a reference voltage V 1, when the voltage of the capacitor exceeds the reference voltage V 1, the potential of the output end of the voltage comparator turns over, the MCU generates interruption, the timer is stopped to count, a first sampling time t is obtained, and a sampling time value t is in direct proportion to an analog sampling resistance value;
Step 3, after time delay t 2, repeating the step 1 to rapidly discharge the fixed capacitor, and repeating the step 2 to acquire the next sampling time value t;
and 4, acquiring capacitor charging time according to a certain sampling time interval, acquiring a sampling time value acquired at intervals, and acquiring an analog quantity taking time as a reference based on the fact that the sampling time value is in direct proportion to the resistor.
3. The method for collecting the low-frequency analog quantity sampling circuit based on the resistive sensor according to claim 2, wherein the method comprises the following steps: in the step 1, the step of rapidly discharging the fixed capacitor includes that the MCU sets the I/01 port to be in a quasi-bidirectional mode, and pulls down the I/01 port, the fixed capacitor is in a short circuit state to the ground, the fixed capacitor is rapidly discharged, after time delay time t 1, voltage drop at two ends of the capacitor is 0 volt, and the discharge of the fixed capacitor is completed.
4. The method for collecting the low-frequency analog quantity sampling circuit based on the resistive sensor according to claim 2, wherein the method comprises the following steps: the sampling time interval T should be greater than the time T required for the RC charging circuit to charge from 0 volts to V 1, the sampling time interval t=t 1+t+t2, and the voltage V 2 of the constant voltage source should be greater than the reference voltage V 1.
5. A low-frequency analog sampling circuit based on a resistance type sensor is characterized in that: the constant-voltage power supply comprises a sampling resistor, a fixed capacitor and an MCU, wherein a timer is arranged in the MCU, one end of the sampling resistor is connected with a constant-voltage source, the other end of the sampling resistor is connected with the fixed capacitor, the sampling resistor and the fixed capacitor are connected in series to form an RC charging circuit, the MCU is provided with an I/01 port input port, and a non-grounding end of the fixed capacitor is connected with the I/01 port.
6. A low-frequency analog sampling circuit based on a resistance type sensor is characterized in that: the device comprises a sampling resistor, a fixed capacitor, a switching triode, a voltage comparator and an MCU, wherein a timer is arranged in the MCU, the switching triode is connected with the fixed capacitor in parallel, and a base electrode of the switching triode is connected with an I/01 port of the MCU through the resistor.
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