1-Wire Energy Management Projects

Home Telemetry and Control Systems to Monitor and Reduce Energy Costs

  DS2408 Board

The Maxim 1-Wire DS2408 chip is a 8 channel addressable switch. While this chip has many uses it's most useful in expanding the output/input ports of a microprocessor. Some of the features of the device include:

  • On resistance of the PIO pull down transistor is 100 ohms.
  • Unique, factory-lasered and tested 64-bit registration number. No two part registration numbers are alike!
  • 2.8 to 5.25V DC single voltage supply operation
  • Operating temperature range of -40F to +185F

Pictured above is the DS2408 board (pre-production) with six out of eight I/O boards plugged-in.

  • The first board (position 7, bottom right) is an early mechanical relay board
  • The next three positions (6, 5 and 4) have "LED Only" boards used for testing (they do include the 10K Ohm pull-up resistor also)
  •  Position 3 is empty
  • Position 2 has a Solid State Relay (SSR) (red LED) board
  • Position 1 has a Isolated Input board using a standard 4N25 chip
  • Position 0 is empty

Note on the design of this board:

The DS-2408 chip requires a 10K Ohm pull-up resistor on every port (eight ports) or the chip outputs "float" (between 1 and 0 or On and Off)

I'll bet I spent a week or more (after I had the software working correctly) trying to figure out why the chip would not return a 1 or 0 status reliably. The status would "float" each time I took a reading!

This is because the standard "Off" status of each port is "High" or 1 and the 10K ohm pull-up resistor (tied to +5VDC) forces the port "high". When commanded the chip can easily pull the port "Low" or 0.

Other features of this DS2408 PWB (pre-production) include:

  • 24V AC input via screw terminal block. The power is then routed up to the IO Boards attached.
  • Secondary 5V DC supply voltage capability
  • Alternate DC voltage supply to IO board
  • Power status LED positions
  • DIN Rail mounting
  • Boards inter-connect to each other in-line on the DIN Rail
  • Up to four different channel use selections per board
  • Supports "house" or "alternate" power supply options per board
  • Supports voltage stabilizing capacitor *
  • Supports pull-up resistor *
  • Supports clamping diode *

* - usage suggested when boards are separated by long distances (like 20 feet or more) due to signal strength issues over long distances of copper wire.

Pictured above is the DS2408 prototype board and includes the mechanical relay prototype and the isolated input prototype.

 If you focus on the center of the picture, that's a carrier package for the DS-2408. Since the DS-2408 chip is a "gull-wing" design and not offered in a standard "dip" package I had to purchase a carrier for the device, cost about $100. Without the carrier, it's next to impossible to test like this.

Also notice all the resistors. Those are the 10K Ohm pull-up required to make the device read reliably over and over again as mentioned above.

Again, this board is still a prototype. When (and if) we go to production we will add the capability for DIN Rail mounting and board inter-connection on the DIN Rail (end-to-end). 

The inter-connect would support:

  • 5V DC power
  • Ground
  • Four (4), yes 4, 1-Wire data lines, pick one
  • 24 V AC power distribution
  • Alternate 5V DC power
  • Alternate DC voltage (like 12V DC or 16V DC, whatever your design needs)

Below is a picture of the inter-connect capability on a DIN Rail. (this will eliminate lots of wiring headaches!) 

 

Wire Length

The other advantage of these devices is the distance you can run the wires (phone cord) from the controller.

Sources on the internet claim 1-Wire devices support distances of thousands of feet. I've not tested that but so far my shorter distance tests have been successful.

In my project I plan on running about a dozen temperature sensors with wire lengths of about 300 total feet. (This is not as easy as it sounds but we'll discuss that in my "Timeline" articles)