1-wire info and recommendations

[nking]

Thanks Gina - yet another project to look forward to.....

[Gina]

One thing I've discovered in setting up my 1-wire network is that although you can get RJ11 plugs to work with RJ45 sockets, they are too loose a fit for a reliable connection. Think I'll post this in the General Forum too as it applies more widely than just 1-wire.

[Gina]

Having got my 1-wire network and sensors working and software logging the results, I've found a niggling problem with the DS18B20 temperature sensor. They are prone to an occasional error resulting in a reading of 85C. I guess I shall have to detect this and re-take the reading when it occurs. I'm rather disappointed - I din't expect this sort of thing from a professional component. This is not just a bad sample - I've Googled the problem and found several references to it. There are other 1-wire temperature sensors but they are not as convenient to use and I have bought several DS18B20 chips with the intention of measuring several different temperatures.

So it's not just Fine Offset stations that suffer from temperature spikes!!

[Gina]

I now have a working 1-wire circuit for my new wind sensors. It uses the usual reed switch and magnet for the anemometer but optical encoding for the wind vane (I was unable to produce an effective read switch version). I have overcome the need for more current than available parasitically from the 1-wire network by switching the LEDs on only during the reading process. A fairly large electrolytic capacitor supplies the LED current for the short period they are on, being recharged in the off period.

1-wire_vane_optical_gray-11-02-21.png

The anemometer reed switch is connected to a DS2423 counter chip which accumulates counts - 2 per revolution of the anemometer rotor. The count is then read periodically to determine the wind speed (and wind run). Circuitry to remove switch contact bounce is provided within the DS2423 counter chip.

For the wind direction :- A DS2413 dual PIO chip is used to switch the LEDs and the current in the photo-transistors produces a voltage across individual resistors and the 4 voltages are fed into a DS2450 4 channel analogue to digital converter chip. Using analogue sensing allows variation in light levels, sensitivity and opacity of the encoding disc to be allowed for in the software.

Power to the ancillary components, DS2423 counter and DS2450 A/D is provided parasitically from the 1-wire network by a Schottky diode and reservoir capacitor. The latter is made big enough so that the voltage only drops by a couple of tenths of a volt when the LEDs are on. Another Schottky diode is connected across the 1-wire network to trap possible negative going spikes on the line. This is standard procedure to protect the chips.

[Gina]

Here's a better diagram...

1-wire_wind_optical_11-02-21.png

[Charlie]

Hi Gina,
I was surprised to hear about your temperature reading problem with the DS18B20 as I have not seen it before. I did some poking and I guess it's been around since 2004. It's not clear if it was fixed in later versions or not. At any rate, the issue seems to be with the power up reset. There is supposed to be a simple work around that involves resetting the chip at least once before taking the reading. The example I found says this should work:
> Reset
> ROM Command (Skip, Match)
> 0x64
Since I can't reproduce it on my devices (tried 2) I can't comment on whether or not the workaround actually helps, but I thought I'd pass it along.

[Gina]

Thanks Charlie I'll check that out. Not really a problem - if I get 85C I just use the previous good reading. Much less of a problem than random spikes from the FO unit.

[Gina]

Wind sensors 1-wire interface showing chip pin numbers:-

[Gina]

I've now received an RH sensor I ordered a few days ago. The sensor is a Honeywell HIH 4030 SMD ready mounted on a breakout board with 0.1" pitch connections. I found a supplier in the UK. http://www.active-robots.com/products/s ... sors.shtml Second item on the page. This was the cheapest supplier I could find in the UK. Total cost including delivery and VAT came to £16.84.

I shall be constructing a 1-wire interface as below but the Schottky diodes are individual diodes obtained from Sheepwalk Electronics and the humidity sensor is a later version. The DS2438 measures the humudity sensor output, the supply voltage and the temperature from which the relative humidity can be calculated. Also, there is no need for a separate temperature sensor as there is already one included.

1-wire_humidity.gif

[Charlie]

Hi Gina,

I came across this old thread while doing a search - where did you ever get to with this project?

[Gina]

I'm afraid I haven't been on here for a while and also my weather station development has been on hold for a year or so as I've been concentrating on astronomy and in particular, astrophotography. But I'm going back to 1-wire for temperature and humidity sensors for cooled DSLR cameras. I'm also expecting to get back to my weather stations soon. As I recall, I got the 1-wire sensors all working but need to write the software to interface the sensor data with the data processing display and upload routines that I'm using with the Fine Offset weather station. There is also more I want to do on the web site and displays.

Currently I'm sorting out my various computers and the weather website is not being updated. I also need to repair the 1-wire anemometer as it got damaged in a very bad storm.

[pete_c]

I've seen similiar with use of multiple 1-wire sensors in a laboratory environment. The price point of the sensors allows for multiple sensors at a reasonable cost.

In the current home I have temperature/humidity sensors in every room of the house. Its also a hodgepodge of multiple networks and multiple devices kind of done up in a hub and spoke methodology. Today for most of the DB / Charting I utilize SQLite running on Wintel and our Linux boxes collectively gathering data via multiple xAP instances.

Trying a new / old similiar to but not a Maxim USB 9097. It is using the Maxim 1-wire technology but comes in a "kit" using standard 3 pin cabling which can be daisychained and sensors come with shielding et al.

For a bit in UV calculations I was using the 1-wire light sensors and calculating a UV 1-16 number which kind of worked; then went to the temperature sensor in a sealed jar method.

http://www.pcsensor.com/index.php?_a=vi ... oductId=52

[PhaedrusUK]

[apologies to all for being (slightly) off topic- newly registered not allowed to PM]
Not sure about the 1 wire, but good to know you`re still knocking about Gina and looking forward to your weather station update

[Gina]

Thanks Trev (it is you isn't it?). Been swapping about with computers and things aren't yet all set up on this one.

[Gina]

Hi folks I'm back and still working on various electronics projects including this one though it's been "on the back burner" for quite some time now. I'm hoping to resurrect it very soon and have been looking at a wall mounted display in my living room. A lot has happened since I last posted and I'll post updates shortly.