This kit has been discontinued. Over the years we have developed many improved designs.
This design is being used in the International Space Station.
Documentation (without Figures).
We have completed the development a kit capable of addressing up to 256 DS1820 temperature sensors with optional range extension to 1000 feet, performing 12-bit A/D measurements on eleven channels and providing eight general purpose I/O leads.
Note that this is a kit, intended for initial assembly on a solderless breadboard. You might later decide to make it more permanent.
The price for the basic K256 package is $49 and includes;
1 PIC16C73A (28-terminal DIP) 1 DS1820 Digital Thermometer 1 DS275 RS232 level shifter (8-terminal DIP) 1 24LC16B EEPROM (8-term DIP) 1 TLC2543CN 11-channel 12-bit A/D (20-pin DIP) 1 4.0 MHz Resonator 1 LED, 5V 1 SIP Resistor Network 10 330 Ohm 10 10K 10 100K 10 0.047 Cermic Caps 1 Morgan Logic Probe Wire Documentation(For the many thousands who have purchased our current temperature kits, the upgrade price is $34. Note that this system is for DS1820s only. (not DS1821s).
When running the DS1820's in the extended distance mode (1000 feet) you will need one dual bidirectional current gain amplifier (8-pin DIP) at the PIC and one at the distant end of two runs. These are $12.00 for three.
Note that the kit includes only one DS1820. Additional DS1820s are $5.50.
Unlike other similar units, this is reasonably priced, has far more capabilities and may be controlled using any RS232 serial port. This might be UNIX, DOS, Windows, Mac, a modem, terminal node controller or standalone terminal. The interface is simply one of sending and receiving character strings. The "smarts" are in the PIC.
To my knowledge, this is the only package which uses bidirectional current gain amplifiers to provide for reliable operation at distances of 1000 feet or more.
Note. We do not provide software for the workstation, PC or Mac or whatever. This kit is for tinkerers who want to write software to meet their specific application. Testing is facilitated by manually typing commands using HyperTerm or equivalent.
As with all of our kits, if you are not satisfied, simply return it for a full credit.
Temperature.
Up to 64 DS1820s may be daisey chained on a single run or bank. Note that this consists simply of a twisted pair; signal and ground. The unit. provides for four of these banks. Thus, up to 64 sensors on each of four runs or a total of 256 sensors.
An option strap is provided to permit all four runs to operate in the parasite mode or to have two runs operate in the parasite mode and two runs in the extended range mode.
Note that you need not fully populate a run nor use all of them. You might have eight on one run throughout the house, two on another run in the basement, a run to the attic with a single sensor and a run outside with two sensors.
When in the parasite mode, the run consists simply of signal and ground. Power for the remote sensors is derived from the bus. When operating in the parasite mode, I would recommend the total length of the cable on any run not exceed 200 feet.
When in the extended range mode, +5VDC must also be supplied to each remote sensor. This may be done by running an additional conductor or it may be locally supplied at the remote location. The extended mode also requires a dual bidirectional current amplifier at the PIC and one at the distant end of each of the extended runs.
For example, you might use two of the runs in the parasite mode to monitor temperatures throughout the house and use the two extanded runs to monitor the temperatures in a 1000 foot distant barn to the north and a 1000 foot distant green house to the south.
I am uncertain how far one can go in the extended mode. I tested this with 1000 feet of cable on a spool with 32 sensors at the distant end and it worked reliably.
The PC initializes the system by issuing the "I" (as in "Init") command. The PIC then performs a binary search for all devices in each of the four banks (runs) and returns;
000 1034456c3 000000e8 001 1034457d3 000000c4 002 10500a2c3 0000003a 100 1034455d3 000000aa 101 10355d456 00000089 200 1024cab2f 000000cc
Note that in this case, three devices were found in bank 0, two in bank 1, 1 in bank 2 and none in bank 3. Note that the unique 64-bit serial number associated with each of the DS1820 is returned in two fields. This provides the user with a cross reference which is important as the PIC does the assignment of the device number. This will not change if the system configuration does not change, but may change as 1820s are added or removed.
That is, 1034457d3 000000c4 may always in the wine cellar and for now it is known as 001. Howver, if you add a device on the same run in the turnip bin having a serial number which is less than this, it will assume either the 000 or 001 designator and the wine cellar will become 002.
Measurements may then be made by issuing the 'T" command followed by the three digit hexadecimal designator of the form;
Tbddwhere b is the bank and is in the range of 0 - 3 and dd is the device number in the range of 00 - 3f.
For example;
T001 // T followed by the three digit desigand the unit will respond;
T001 23.78 1034457d3 000000c4where the first field is the designator, the second field is the temperature in degrees C and fields three and four are the serial number.
The temperature is in signed decimal (-55.00 to 125.00) with two places after the decimal point. Resolution is 0.035 degrees. Accuracy is 0.5 degrees C.
A/D Measurements.
Measurements may be made by issuing the "A" command followed by the channel which is in the range 0 - A. (11 channels).
A9 // channel 9and the unit will respond;
A9 1028where field two is the A/D reading in decimal in the range of 0 to 4095. The voltage may then be calculated as (band/4096) * (Vref+ - Vref-) + Vref-.
For example, if Vref+ is at 5.0 and Vref- is at ground (0.0);
V = band / 4096 * 5.0IO Bits.
A bit may be output to a logic one or zero (<0.4 VDC) by using the "S" (set) or "C" (clear) command. Note that a logic one is a high Z which permits you to add a pullup resistor to interface with devices requiring other than TTL levels.
For example;
S5 // exert an output one on bit 5The unit responds;
S5 1Another example;
C3The unit responds with;
C3 0Any bit may be read using the "R" command;
For example;
R2 // configures bit 2 as an inputThe unit responds;
R2 0meaning that bit 2 is at a logic zero.
Note.
We try. And, we try to honestly represent the capabilities of all of our kits.
The whole subject of the length of runs to DS1820 sparks controversy. I feel that a 200 total feet limitation on a run operating in the parasite mode is conservative. When operating in the extended mode with the bidirectional current amplifiers, I feel 1000 feet is conservative. Hopefully, you can go much further in both cases. But, if you have an arc welder generating noise or a ham radio running the full limit on 160 meters, there may be problems.
This is an inexpensive kit for hobbyists who are willing to experiment. In providing the four runs and in providing the option for parasite or extended mode, my feeling is that we are giving you more tools than anyone else in meeting your objective.
But, if you are a contractor looking to drill the holes, run the wire, solder in the sensors, put up the sheetrock, paint and paper and only then test the operation, this package isn't for you.
Pricing.
For breadboarding you may wish to purchase;