Strange outside temp readings

[malc-c]

I have one of the Maplin fine offset stations and up until the past few days it's been running fine. However I noticed that the wind speed sensor was no longer revolving the other day, and today, whilst I still have frost on the patio table, the sensor is reading 10.5C for the outside temperature,and the sun has just set. I've replaced batteries in both transmitter and base station (less than 20 feet apart), but the readings are still high. The BBC website gives the current temperature at 3c.

I can't do much about replacing the wind sensor until a friend with a long ladder and head for heights is free to help me out as the sensors are up high



Anyone have any suggestions as to how I can get the readings to show correct temperatures, other than replacing the transmitter unit. Do the thermistors fail and are they replaceable ? - It's a shame they don't use one wire devices such as the DHT11 or DS18B20's - I have stacks of them around !

Also noticed the humidity is reading 34% - external websites state 88% - ???

[malc-c]

OK... tried a longer period with batteries removed...

Initial power up and it read 4.2c and 45% humidity.... but then slowly increased, 6.6c, then 7.9c now 8.3c and humidity dropped to 35% again....

[AllyCat]

Hi,

Where is the transmitter located, I can't see it on the mast and you say you've changed the batteries? Have the Wind/Rain cables been extended?

The solution may depend on the age of the station, because the design was changed about 3 - 4 years ago (but Maplin didn't alter their model number). The "old" versions did use a thermistor (which might be replaced) but the main issue was that any leakage current in the WIND cable (due to moisture in the cable/connectors) could produce crazy External temperature measurements. So try unplugging the Wind cable and see if the temperature is still wrong.

However, the later stations don't appear to use a thermistor but take the temperature and humidity from the same module, which AFAIK has not been identified as an "off the shelf" spare part. However, the whole transmitter may (still) be available as a spare part from Maplin (their part number is important and most of their web "Q&A"s are misleading or wrong!). There are also other sources of spare transmitters, but you need to ensure that it's a 434 MHz radio version (many now are 868 MHz).

Cheers, Alan.

[malc-c]

Thanks for the reply,

The transmitter is located in a shaded area on the side of a shed. However, that's not the problem as I swapped over both wind sensors for new ones, and brought the transmitter inside and placed it along side the base station so I can compare temperatures and the "outside" reading was still around 6c higher with humidity half the value read by the base station.

I looked at Maplins site, and read the questions as there is a lot of confusion over the frequencies. My base station is black and states its N96GY at 433.9 MHz, and the outside transmitter is a grey plastic enclosure where some seem to be a cream coloured version. But the information on the website seems to suggest that the current spare part is 868 MHz... I know it's only £15 for the part, but they are selling the complete package for £59.99 so I wouldn't want to spend 25% of the cost for something that wouldn't work and then have to go through the hassle of returning it. Thing is I already have spare rain gauges, wind sensors and a base station that functions perfectly...

I took a look inside the transmitter and it has the later version of sensor, the small which two pin module on a small daughter board, not the small blue theremister that the originals had. If anyone knows of an alternate source for a 433Mhz transmitter I would welcome a link

[malc-c]

Ok this is really strange. This morning I disconnected and reconnected the batteries in the transmitter and left the pcb on top of the display of the base station (I have wired a remote battery pack which normally sits in the shed) and let it settle for a while. After a short period both temperature readings were within 0.1c of each other and stayed more or less like this for the rest of the morning. I've now moved it back outside and without any of the other sensors connected it's reading 2.4c and 50% humidity (its very foggy here in Stevenage so I doubt that the humidity is correct). Checking with the local weather forecast online, temperature at 14:00 was 3C and 99% humidity, so whilst temperature might be spot on, humidity is way out, but I can live with that as outside temps are more important to me than humidity

So, no idea what happened there. Yesterday, when the batteries were connected the temperature would display the correct temperature and then rise at each transmission until it was around 7-8 degrees higher than the correct temperature, today it was the reverse, started at around 10c and has dropped and stabilised at around the correct temperature over the past 20 minutes or so.

Once my friend can spare some time to replace the stuck wind speed sensor on the roof I'll connect that up to see if that makes any difference, and then connect the rain sensor again. Hopefully the station will be back up and running to start a new set of data for 2017.

[AllyCat]

Hi,

It might be the present high humidity condensing on the PCB and producing erratic readings (corrected when brought indoors). OR the Humidity sensor (which also supplies the temperature) might be failing !

I'm reasonably confident that ALL Maplin stations have used 433.9 MHz. However, a few have no Wind Vane, so the replacement transmitter is cheaper but is NOT compatible with the other stations. Therefore the £15 one (if they have stock) should be compatible with your station. If you have a nearby Maplin's (and there is stock) it might be worth a try as they should accept a return/refund if it doesn't work (particularly if you state exactly what it's for.) They are significantly cheaper (sometimes very much so) for FO spares than any other UK supplier I know of.

Cheers, Alan.

[malc-c]

Thanks Alan,

Whatever it was it's now reading realistic temperatures and humidity. Maybe anyone else experiencing similar issues might try the same thing before replacing the transmitter unit.

My mate is swapping out the wind speed sensor this lunchtime so hopefully the temperatures remain the same when that's plugged back in, fingers crossed

[malc-c]

Well here's a small update....

After my last post the readings soon crept up again, so I pulled the batteries and basically gave up trying to resolve it. I tried again back in the summer, with fresh batteries etc and the problem was still present, and Maplin were out of stock of the replacement transmitter unit, and have been for ages.

Fed up with missing out on new data when we've had the recent high winds, or cold snaps I thought about re-instating the weather station, however I don't want to buy another complete kit as I still have all the spare sensors from the second kit, and the LCD touch screen works fine. So I spent the afternoon googling various sites and eventually came across one shop that stocked replacement transmitters for the Watson WH1080 and similar units. I described the board, the markings on the crystal and that it had a 14B in marker pen scribbled on it, which was all the info he needed. So for £19:96 plus postage one was duly ordered, and should be here in a couple of days given the snow has had a knock on effect for deliveries.

I'll update this post with my findings, and if it works and remains stable I'll post details of where I obtained the module from.

[malc-c]

Well excellent service from Radio World. Their Watson 8681-HHT Pass 14 replacement sender using arrived via 1st class recorded delivery this morning. Installed the batteries and re-booted the base station... held my breath

After a second or two the outside temperature and humidity was displayed on the LCD panel. I connected the wind and rain gauges and data began streaming through... So after struggling for almost a year without a weather station I am now back up and running

There are two variants in the 433 Mhz range, pass 7 and pass 14. You should be able to identify what protocol yours is via a small green label inside the battery compartment. If this is missing, then check the PCB in the sender as most have the version written on them in marking pen. Mine had 14B written on it.

My replacement cane from RadioWorld (https://www.radioworld.co.uk/) and cost £16.63 plus post and VAT (£22.95 inclusive) and if you order before 12:00 noon you should be able to receive it next day.

I'm now a happy bunny