JPS59154366A - Measuring device provided with microcomputer with a/d conversion function - Google Patents

Abstract

PURPOSE:To correct automatically the A/D conversion error of a microcomputer with an A/D converter by connecting a voltage dividing circuit of a correcting voltage parallel with a measuring circuit to the A/D converter through a switch. CONSTITUTION:Instead of a measuring circuit 4 including a sensor whih connects a switch 3 to a contact K2, a voltage dividing circuit 5 of the correcting voltage parallel with the circuit 4 is connected to an A/D converter 2 of a microcomputer 1. An A/D-converted digital reference voltage and a regular digital reference voltage which is set preliminarily in the computer 1 in accordance with the reference voltage are compared with each other to determine the error of the converter 2. The error of a digital measured voltage, which is attained by the circuit 4, due to the converter 2 at the time, when the switch 3 is connected to a contact K1, is corrected automatically in accordance with this determined error by the computer 1, and the A/D cnversion error of the microcomputer with the A/D converter is corrected automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a measuring device equipped with a microcomputer with an A/D conversion function, and more particularly to an automatic correction method for A/D conversion errors.

<Prior art> For example, as the functions of consumer electronic devices such as electronic registers become more diversified and their performance becomes higher, A/ Some devices have a built-in microcomputer with a D conversion function. In such electronic equipment, there is a 7＼ fluctuation in the Δ/D conversion accuracy, and the accuracy of the Δ/D conversion is higher than that.
If conversion is to be performed, it is necessary to correct errors during A/D conversion.

FIG. F shows a circuit diagram of a conventional example. A microcomputer with A/D conversion function is equipped with external terminals for analog signal capo 1-, A/D conversion reference voltage ref, and external power supply Vdd, and sensors RT such as thermistors are used for error correction. It is connected in series with a variable resistor RV and a fixed resistor R1, a reference voltage Vref is applied to all the series circuits, and a sensor output is connected to input ports 1 to 1. In such a measuring circuit, the voltage Vkl input to the input capacitor K+ is stored in RAM (random access memory).

However, in order to correct the A/D conversion difference, the variable resistor R
t must be adjusted.

To explain this adjustment method, first, a reference resistor Rd is connected in place of the sensor RT, and the value of the variable resistor RV' is adjusted so that the voltage of 1 becomes a predetermined value Vkl' at the input port.
Determine. However, this method not only requires the above-mentioned adjustment work, but also causes errors in the adjustment work, and furthermore, errors due to aging during use intervene.

<Objective of the Invention> An object of the present invention is to provide an electronic device that eliminates the labor of the above-mentioned adjustment work and automatically converts A/D conversion errors using a microcomputer.

<Configuration of the Invention> To summarize, the present invention omit the adjusting variable resistor RV provided in the conventional sensor voltage detection circuit, and apply a predetermined calibration reference voltage Vk2 to the second input port I (2). The computer reads the digital value converted by an A/D converter built into the microcomputer, and corrects the converted value to the digital value of the sensor output in accordance with this value.

<Example> The present invention will be explained in detail below.

FIG. 2 shows a circuit diagram of an embodiment of the present invention. 2 (The signal on the input port K1.i<' of IM+ is introduced to the common A/D converter 2 via the switching circuit 3, and this switching circuit 3 is connected to the CPU C central processing unit in the microcomputer 1.) It is switched by the command.

The external circuit of the microcomputer includes a correction voltage dividing circuit 5 consisting of a series connection of resistors Ra & Rb in parallel with a measurement circuit 4 consisting of a series connection of a sensor RT and a resistor R1.
The output end of the sensor RT is connected to the input port +, and the voltage dividing point of the voltage dividing circuit 5 is connected to the input port -1-2.

It is assumed that the microcomputer 1 has, for example, an 8-bit configuration, and the built-in A/D converter 2 has a resolution of 28-256. In addition, this A/D converter 2
is assumed to have an error of the lowest bit. Also, the resistance Ra of the voltage dividing circuit 5.

It is assumed that the error due to the variation in Rb is sufficiently smaller than the error of the A/D converter and can be ignored.

Therefore, the ratio of the resistance values Ra and Rb is set so that the voltage at the voltage dividing point of the voltage dividing circuit 5 is equal to the analog input voltage value of 011''. Setting the divided voltage in this way Therefore, if you first switch the switching circuit 3 to the 2nd side and set the A/D conversion output, the A/D conversion when switching the switching circuit 3 to the 1st side will depend on the magnitude of the value. The output value can be corrected.In other words, the value of the lower 3 bits of the A/D conversion output when switching to the K'2 side and the value of the lower 3 bits of the A/D conversion output that should be corrected during measurement.
6 Errors for focus resolution are as shown in the table below.

However, 1 unit is 1/2 of the maximum output of the A/D converter.
It is 56.

Output of measurement circuit 4 (input capo) K+ voltage V
kl is, and the value after this is digitally transformed by the A/D converter 2 is, for example, n=126, and the A/D conversion output of the voltage Vk2 of 2 is applied to the input port at this time, for example. “
If it is 100'', it can be seen from Table 1 that the Δ/D conversion error is output in excess of -1 unit, so the corrected measurement value will be n-125.

Note that the switching circuit 3 of the present invention may be provided outside the LSI, and in that case, the input ports + and 2 are located outside the LSI.

<Effects of the Invention> According to the present invention, it is no longer necessary to adjust the A/I converter by adjusting a variable resistor as in the prior art, and the manufacturing process is streamlined. Further, since automatic correction is executed automatically or manually as needed, high measurement accuracy can be maintained at all times.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional example. FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation of the present invention. 1 Microcomputer 2-A/D converter 3-Switching circuit 4-Measuring circuit 5-Correction voltage voltage dividing circuit Kl, 2-Human power boat Vref-A/D conversion reference voltage Patent applicant Sharp Corporation Company agent Patent attorney Nishi 1) Arata

Claims (1)

[Claims] 2 analog voltage input ports (Kl, 2), A/D
A microcomputer equipped with a conversion reference voltage terminal and a Δ/D conversion block that converts the input voltage of either of the above two input ports into a digital signal, and a microcomputer that converts the output voltage of the sensor to one of the above two input ports. A measurement circuit that introduces the voltage at the reference voltage terminal into one, and a correction voltage divider circuit that introduces the correction reference voltage obtained by dividing the voltage of the reference voltage terminal into a predetermined ratio into the remaining terminal of the input capo-1- of the 21IIIJ. The output voltage of the sensor is adjusted according to the magnitude of the digital value when this correction voltage is input to the A/D conversion block described in L. A measuring device equipped with a microcomputer with a Δ/D conversion function configured to perform correction.