e01ch14.PDF

(121 KB) Pobierz

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

SMALL CIRCUITS COLLECTION

014

Remote ADC with RS232 Output

K. Haddad Shargh

When the conversion is completed, the INTR pin is acti-

vated and valid data will be saved in 74F374. Next, this data

is copied into a shift register for parallel-to-serial conver-

sion. This shift register consists of two cascaded 74F166’s

(IC5 and IC6). The first and tenth cell of this register chain

are connected to ground and Vcc respectively for produc-

ing the start bit and stop bit.

In this circuit a 555 IC is used as clock generator. The

555 is configured as a bistable multivibrator for generating

a 110-Hz square wave. It is recommended to check this fre-

quency and make sure it is within 2% tolerance. If desired,

the oscillator frequency may be changed by modifying the

values of C3 and R4.

A programmable down counter type 74F169 (IC4) is

used to generate the Load signal for the shift registers. This

IC is pre-loaded with the value 10. Consequently it gener-

ates pulses for loading IC5 and IC6 at every tenth clock

pulse.

The last stage is the RS232 line driver, which shifts the

TTL level to +12 V and –12 V while also matching the line

impedance. Here, the well-known MAX232 is used in its

standard configuration.

A ‘Null Modem’ connection must be used to establish

The circuit converts an analogue voltage to its digital

equivalent which is transmitted to a PC via an RS232 link.

This type of circuit is useful for controlling remote equip-

ments using only one PC. For example, you can monitor

several furnaces by sending their individual temperatures to

a central PC. In combination with a simple program the

ADC lets you decide which action must be taken when cer-

tain temperatures are measured.

This circuit is composed of three building blocks. The

first one handles the conversion of analogue signals to dig-

ital data. The second block accepts the digital data and

puts it in the standard RS232 data frame before converting

it to a bit stream. The last function is the RS232 line driver.

The familiar and low cost ADC0804 is used as ADC in

this circuit. This IC converts the analogue voltage in the

range of 0 to 5 volts into digital data by means of a 256-level

quantisation process. Alternative ICs may be used but you

have to consider the communication line capacity.

The ADC0804 is configured as free-running converter.

Unfortunately, in this mode, when the conversion is in

process, invalid data appears on its data bus. This problem

is solved by using a 74F374 octal latch on the data outputs.

+5V

C7

+5V

R1

1

µ

IC2

K1

IC5

20

2

74F374

14

13

V+

1

16

1

C1+

6

18

17

16

15

14

13

12

11

18

19

16

15

12

12

C5

VI+

DB0

DB1

DB2

DB3

DB4

DB5

DB6

DB7

6

17

11

IC7

9

3

2

1 µ

VREF

C1–

14

10

IC1

11

14

7

T1IN

T2IN

T1OUT

T2OUT

R1OUT

R2OUT

R2

10k

13

5

19

10

13

7

3

CLKR

8

9

6

5

2

4

12

8

ADC0804

R1IN

7

3

2,3D

4

8

9

4

CLK

R2IN

4

2

2,3D

1

2

4

C9

9

CS

RD

C2+

3

1

C6

1D

1,3D

5

MAX232

4

µ

7

7

5

7

5

15

1 µ

VI–

INTR

C2–

≥

1

D9

C3/1

C2

8

3

11

6

V-

C1

DB9

AGND

WR

C1

1

6

EN

M2[LOAD]

C8

10 µ

150p

15

M1[SHIFT]

10

9

R

1

µ

SRG8

DB9

DB9

74F166

LM336

IC4

zero - modem

+5V

CTRDIV16

M1[LOAD]

1

DCD

DCD

1

+5V

9

6

DSR

DSR

6

R5

M2[COUNT]

2

RxD

RxD

2

1

IC6

SRG8

M3[UP]

7

RTS

RTS

7

4

8

9

M4[DOWN]

R

3

TxD

TxD

3

15

7

R

10

15

G5

G6

3,5CT=15

M1[SHIFT]

DIS

8

CTS

CTS

8

R4

7

IC3

4,5CT=0

M2[LOAD]

4

DTR

DTR

4

3

2

6

OUT

2,3,3,6+/C7

≥

1

9

RI

RI

9

C3/1

6

555

7

THR

2,3,3,6–

5

GND

GND

5

2

TR

1

2

1,3D

2,3D

CV

3

4

5

6

14

[ 1 ]

[ 2 ]

[ 3 ]

[ 4 ]

1,7D

5

1

13

+5V

3

4

5

C3

C4

2,3D

12

+5V

5V

+5V

11

100n

100n

20

16

16

16

10

74F169

IC2

IC4

IC5

IC6

11

12

14

10

8

8

8

13

74F166

014125 - 11

40

Elektor Electronics

12/2001

855733951.131.png

855733951.142.png

855733951.153.png

855733951.164.png

855733951.001.png

855733951.012.png

855733951.023.png

855733951.034.png

855733951.045.png

855733951.056.png

855733951.067.png

855733951.078.png

855733951.089.png

855733951.090.png

855733951.091.png

855733951.092.png

855733951.093.png

855733951.094.png

855733951.095.png

855733951.096.png

855733951.097.png

855733951.098.png

855733951.099.png

855733951.100.png

855733951.101.png

855733951.102.png

855733951.103.png

855733951.104.png

855733951.105.png

855733951.106.png

855733951.107.png

855733951.108.png

855733951.109.png

855733951.110.png

855733951.111.png

855733951.112.png

855733951.113.png

855733951.114.png

855733951.115.png

855733951.116.png

855733951.117.png

855733951.118.png

855733951.119.png

855733951.120.png

855733951.121.png

855733951.122.png

855733951.123.png

855733951.124.png

855733951.125.png

855733951.126.png

855733951.127.png

855733951.128.png

855733951.129.png

855733951.130.png

855733951.132.png

855733951.133.png

855733951.134.png

855733951.135.png

855733951.136.png

855733951.137.png

855733951.138.png

855733951.139.png

855733951.140.png

855733951.141.png

855733951.143.png

855733951.144.png

855733951.145.png

855733951.146.png

855733951.147.png

855733951.148.png

855733951.149.png

855733951.150.png

855733951.151.png

855733951.152.png

855733951.154.png

855733951.155.png

855733951.156.png

855733951.157.png

855733951.158.png

855733951.159.png

855733951.160.png

855733951.161.png

855733951.162.png

855733951.163.png

855733951.165.png

855733951.166.png

855733951.167.png

SMALL CIRCUITS COLLECTION

communication between this circuit and computer’s serial

port. For your convenience, the relevant wire connections

between two 9-pin sub-D connectors are included in the

schematic.

Finally, if difficult to obtain locally, the F (fast) ICs in this

circuit may be replaced by LS (low-power Schottky) equiv-

alents.

(014125-1)

855733951.168.png

855733951.169.png

855733951.170.png

855733951.171.png

855733951.172.png

855733951.173.png

855733951.002.png

855733951.003.png

855733951.004.png

855733951.005.png

855733951.006.png

855733951.007.png

855733951.008.png

855733951.009.png

855733951.010.png

855733951.011.png

855733951.013.png

855733951.014.png

855733951.015.png

855733951.016.png

855733951.017.png

855733951.018.png

855733951.019.png

855733951.020.png

855733951.021.png

855733951.022.png

855733951.024.png

855733951.025.png

855733951.026.png

855733951.027.png

855733951.028.png

855733951.029.png

855733951.030.png

855733951.031.png

855733951.032.png

855733951.033.png

855733951.035.png

855733951.036.png

855733951.037.png

855733951.038.png

855733951.039.png

855733951.040.png

855733951.041.png

855733951.042.png

855733951.043.png

855733951.044.png

855733951.046.png

855733951.047.png

855733951.048.png

855733951.049.png

855733951.050.png

855733951.051.png

855733951.052.png

855733951.053.png

855733951.054.png

855733951.055.png

855733951.057.png

855733951.058.png

855733951.059.png

855733951.060.png

855733951.061.png

855733951.062.png

855733951.063.png

855733951.064.png

855733951.065.png

855733951.066.png

855733951.068.png

855733951.069.png

855733951.070.png

855733951.071.png

855733951.072.png

855733951.073.png

855733951.074.png

855733951.075.png

855733951.076.png

855733951.077.png

855733951.079.png

855733951.080.png

855733951.081.png

855733951.082.png

855733951.083.png

855733951.084.png

855733951.085.png

855733951.086.png

855733951.087.png

855733951.088.png

Plik z chomika:

Inne pliki z tego folderu:

bge.jpg (26 KB)
detail1.htm (5 KB)
detail2.htm (4 KB)
detail3.htm (4 KB)
detail4.htm (6 KB)

Inne foldery tego chomika:

Zgłoś jeśli naruszono regulamin