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2 | Howto build a Serial Adapter for Dallas DS1820 temperature sensors | |
3 | ||
4 | Copyright (c) 2001 by Brian C. Lane <bcl@brianlane.com> | |
5 | All Rights Reserved | |
6 | ||
7 | ||
8 | ||
9 | The DigiTemp program for Linux, DOS and Windows 95 uses a simple serial | |
10 | port adapter to communicate with the Dallas DS1820 digital temperature | |
11 | sensors. These sensors use a protocol called One-Wire or Micro LAN | |
12 | (depending on which Dallas documentation you are reading). This protocol | |
13 | requires only a ground and a data wire to the device. All power is derived | |
14 | from the data line while it is idle. | |
15 | ||
16 | The protocol is NOT RS232! The adapter converts the RS232 voltages into | |
17 | the +5v needed to communicate with the DS1820. Each byte sent to the serial | |
18 | port represents one data bit to the DS1820. See Dallas Semiconductor App | |
19 | Note #74 for more information, or the sourcecode for DigiTemp. | |
20 | ||
21 | How To build an adapter | |
22 | ----------------------- | |
23 | ||
24 | If you want a schematic diagram you need to look at page 20 of App. | |
25 | Note #74 from Dallas Semiconductor ( ) | |
26 | ||
27 | ||
28 | Parts List | |
29 | ---------- | |
30 | ||
31 | 1 DB-25 connector or DB-9 connector | |
32 | 1 1.5k ohm resistor | |
33 | 2 1N5818 Schottky Diode | |
34 | 1 1N5228 3.9v Zener Diode | |
35 | 1 1N5234 6.2v Zener Diode | |
36 | 1 2 position terminal block (for connecting the sensors to adapter) | |
37 | ||
38 | Wire cutters and a soldering iron. | |
39 | ||
40 | In this document I will refer to the pin functions. The pin numbers for | |
41 | DB-25 and DB-9 are as follows: | |
42 | ||
43 | Name DB-25 DB-9 | |
44 | ---- ----- ---- | |
45 | DTR 20 4 | |
46 | RXD 3 2 | |
47 | TXD 2 3 | |
48 | GND 1,7 5 | |
49 | ||
50 | NOTE: I have not built a DB-9 version myself. Please let me know if you | |
51 | successfully build one or have problems with it. | |
52 | ||
53 | On the DB-25 pins 1 and 7 must BOTH be connected together. | |
54 | ||
55 | ||
56 | Step Description | |
57 | ------------------------------------------------------------------------ | |
58 | 1. Solder the 1N5228 3.9v Zener between GND and DTR with the | |
59 | Cathode(the stripe) towards DTR. | |
60 | ||
61 | 2. Solder the 1.5k ohm resistor between RXD and TXD. | |
62 | ||
63 | 3. Solder one of the 1N5818 diodes between RXD and TXD with the | |
64 | Cathode(the stripe) towards RXD. | |
65 | ||
66 | 4. Solder the other 1N5818 diode between RXD and DTR with the | |
67 | Cathode(the stripe) towsrds DTR. | |
68 | ||
69 | 5. Solder the 1N5234 6.2v Zener between RXD and DTR with the | |
70 | Cathode(the stripe) towards DTR. | |
71 | ||
72 | 6. Solder RXD to one pin of the terminal block and paint it | |
73 | black. This is the GND connection for the sensors. | |
74 | ||
75 | 7. Solder DTR to the other pin of the terminal block and paint | |
76 | it red. This is the DATA connection for the sensors. | |
77 | ||
78 | ||
79 | There! Now you have an adapter. | |
80 | ||
81 | Connecting the sensors | |
82 | ---------------------- | |
83 | ||
84 | You need to connect to wires to the sensor to attach to the terminal | |
85 | block. If you look at the sensor so that the label is towards you, with the | |
86 | pins facing down the pins are from left to right: | |
87 | ||
88 | 1. GND | |
89 | 2. DATA | |
90 | 3. +5v | |
91 | ||
92 | Solder your wires to GND and DATA and connect them to the terminal block | |
93 | and you're done! Be careful not to overheat the sensor while soldering to | |
94 | it. My method is to tin the legs quickly and let them cool off (while | |
95 | tinning the others) and then to tin the wires, then attach them quickly with | |
96 | a minimum of heat applied. | |
97 | ||
98 | One additional note: Because of the voltage(and current) drop across the | |
99 | resistor this adapter isn't capable of providing enough current to read | |
100 | temperatures above about +70C. This is a limitation of the design, not an | |
101 | error with the DS1820 or the software. | |
102 | ||
103 | If you have any questions or comments, email me at bcl@brianlane.com or | |
104 | subscribe to the digitemp mailing list by sending a blank email to | |
105 | digitemp-subscribe@brianlane.com | |
106 | ||
107 | Brian Lane | |
108 | bcl@brianlane.com | |
109 | http://www.brianlane.com | |
110 | ||
111 | March 13, 2001 |