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AD574 based high-precision digital voltmeter circuit

Published on Feb 11 2011 // Digital Circuits

AD574A American Analog Digital (Analog) introduced single-chip high-speed 12-bit successive approximation type A / D converter, built-in bipolar integrated circuits conversion was mixed films, with fewer external components, low power consumption and high accuracy characteristics, and has automatic zero and automatic polarity function, just add a small amount of resistive and capacitive components can constitute a complete A / D converter, its main features are as follows:
Resolution: 12 bits
Nonlinear error: less than ± 1/2LBS or ± 1LBS
Conversion rate: 25us
Analog voltage input range :0-10V and 0-20V, 0 – ± 5V and 0 – ± 10V two tranches of four
Power supply voltage: ± 15V and 5V
Data Output Format: 12 / 8
Chip operating modes: full-speed mode and single mode

AD574 based high-precision digital voltmeter circuit 1

We use AD574 low-cost high-performance company with the ATMEL AT89C2051 microcontroller to form a high-precision digital voltmeter, electrical schematic diagram in Figure 1, AD574 is a 12-bit successive approximation type A / D converter, a total of 12 data lines, AT89C2051’s P1 and the AD574 high 8-bit data cable directly connecting, AD574’s low 4-bit data lines and the high half-4 MCU P1.4 – P1.7 direct phase, the data read is to rely on the control line SCM time-gating for. P3.5 short period of bytes received AD574 control line (A0), P3.4 then convert the data read control pin (

AD574 based high-precision digital voltmeter circuit 2

), P3.7 work directly with the status indicator side (STS) linked to the structure of such a decision can only be 8-bit output in the form, so

 AD574 based high-precision digital voltmeter circuit 3

AD574A American Analog Digital (Analog) introduced single-chip high-speed 12-bit successive approximation type A / D converter, built-in bipolar integrated circuits conversion was mixed films, with fewer external components, low power consumption and high accuracy characteristics, and has automatic zero and automatic polarity function, just add a small amount of resistive and capacitive components can constitute a complete A / D converter, its main features are as follows:

Resolution: 12 bits

Nonlinear error: less than ± 1/2LBS or ± 1LBS

Conversion rate: 25us

Analog voltage input range :0-10V and 0-20V, 0 – ± 5V and 0 – ± 10V two tranches of four

Power supply voltage: ± 15V and 5V

Data Output Format: 12 / 8

Chip operating modes: full-speed mode and single mode

We use AD574 low-cost high-performance company with the ATMEL AT89C2051 microcontroller to form a high-precision digital voltmeter, electrical schematic diagram in Figure 1, AD574 is a 12-bit successive approximation type A / D converter, a total of 12 data lines, AT89C2051’s P1 and the AD574 high 8-bit data cable directly connecting, AD574’s low 4-bit data lines and the high half-4 MCU P1.4 – P1.7 direct phase, the data read is to rely on the control line SCM time-gating for. P3.5 short period of bytes received AD574 control line (A0), P3.4 then convert the data read control pin (

), P3.7 work directly with the status indicator side (STS) linked to the structure of such a decision can only be 8-bit output in the form, so

Choose end data model can be directly grounded. AT89C2051 only 15 I / O lines, the use of a 11, leaving only four lines, we will output the data through the microcontroller’s serial port output, an external one 74LS164 (the string into and out of) the extended decoder , also shows data for four, the remaining two port lines can not meet the requirements, but also a 74LS138 three – eight decoder to address the display LED strobe.

Here we use the 10V range of the input mode, so the AD574’s Pin13 voltage input for the test, because the only use of an AD574 converter chip, so the CS terminal directly to ground can be. ± 12V power converter voltage supply, operating voltage +5 V.

74LS164 for the string into and out of the decoder, AT89C2051 BCD output through the serial port serial code output by the seven segment decoder 74LS164 BCD, directly with the LED’s a – g is connected, while the four data lines LED correspondence together. LED digital tube used were a male, 74LS138 address code output by a transistor 2SA1015 (PNP) access LED of the common, four LED display is a time-line through the address strobe, and this is our usual dynamic scanning display way.

It is worth mentioning that dynamic scan display, the dynamic scanning have certain requirements for the frequency, the frequency is too low, LED will flicker. If the frequency is too high, due to the short time of each LED light, LED brightness is too low, the naked eye can not see, so generally take 10ms is appropriate, which requires the preparation program, a particular LED strobe to light and maintain a certain amount of time, the procedure often used is to call the delay subroutine. Instruction in the C51, the delay subroutine is quite simple and very easy to change the delay time.

 AD574 based high-precision digital voltmeter circuit 4

AD574 based high-precision digital voltmeter circuit 5