Help with choosing options
Franklin
Posts: 4,747
I have a project I’m working on and need some help deciding the best way to accomplish some of the tasks. It’s a remote weather station (but at this time remote is 500’ or so) with temp, humidity, barometric pressure, wind speed and wind direction.· Several things I’m wondering about are:
1.······ The anemometer has a reed switch that closes twice a revolution so I see the need for a counter but being solar powered and the pulses coming fast I don’t think my best choice is to have the stamp/propeller (haven’t chosen yet) do the counting .
2.······ The wind vane has two continuous rotation pots. Would the stamp be able to get a value if the pot was moving while it was trying to compute? I can use an ADC for this or NDC has a neat chip that takes two 0 to 5v inputs and outputs an ASCII string with the values.
3.······ The data will be compiled into a string and sent out on a radio link to the house where the other link will receive it. The problem here is how do you synchronize the house side to get the message when it does not know when it will come, I’m thinking of sending one packet a minute to save power on the remote end.
I am going to use the temp/humidity module from Parallax and the pressure module from Spark Fun and haven’t run into any problems with that yet except the power for the barometer (it works best at 2.7v) I’m thinking 3.3v and a diode maybe.
Thanks for listening to my rambling and Happy Stamp(propeller..SX)ing
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- Stephen
1.······ The anemometer has a reed switch that closes twice a revolution so I see the need for a counter but being solar powered and the pulses coming fast I don’t think my best choice is to have the stamp/propeller (haven’t chosen yet) do the counting .
2.······ The wind vane has two continuous rotation pots. Would the stamp be able to get a value if the pot was moving while it was trying to compute? I can use an ADC for this or NDC has a neat chip that takes two 0 to 5v inputs and outputs an ASCII string with the values.
3.······ The data will be compiled into a string and sent out on a radio link to the house where the other link will receive it. The problem here is how do you synchronize the house side to get the message when it does not know when it will come, I’m thinking of sending one packet a minute to save power on the remote end.
I am going to use the temp/humidity module from Parallax and the pressure module from Spark Fun and haven’t run into any problems with that yet except the power for the barometer (it works best at 2.7v) I’m thinking 3.3v and a diode maybe.
Thanks for listening to my rambling and Happy Stamp(propeller..SX)ing
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- Stephen
Comments
Jeff T.
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- Stephen
Regarding counting pulses from the anemometer: Because the pulses are coming from a reed switch, there's certain to be some switch bounce. This means that your pulse count will be much higher than it should be, unless you take some measures to deal with the bounce. Since, at two per rev, the counts will be coming quite slowly (from the Stamp's point of view), a simple low-pass filter between the reed switch, with its pull up resistor, and the Stamp input should be adequate to filter the bounce. If you wanted to get fancy, you could even add a Schmitt trigger between the low-pass filter and Stamp input.
-Phil
The remote processor sits waiting for the request. When the remote gets its request it gathers the current data then transmits. Then back to waiting for the next request
House micro waits for the remote string , processes it then continues with whatever it has to do until the next request.
An alternative would be a PC with event driven serial input.
Jeff T.
With regard to (1), I have a writeup on interface to the anemometer switch at www.emesystems.com/OL2wind.htm. There is a schematic there of a debouncer circuit of the sort Phil described. It is true what you say that the COUNT command does take time to capture the data, a couple of seconds at least, to get a good fix on low windspeeds, and that operating time takes power from the battery. The program could COUNT the windspeed less frequently, but given the nature of wind gusts, it is likely to underestimate the maximum windspeed and the total wind run. I designed an independent PIC chip that counts in the background for things like windspeed and rain, so that the Stamp can sleep and then read out the counts. Contact me in PM if you are interested in one of the chips.
With regard to (2), There should not be a problem unless the wind direction is terribly unsettled. It will not change much in the few milliseconds it takes for an ADC to take its reading. Most ADCs have a builtin sample and hold circuit. Are you talking about the dual pot wind vane from Fascinating? The way that works is that you fall back on the reading from the second pot when the first one is in its ambiguous dead zone.
With regard to (3), If the packet comes out at a regular interval like 1 minute, then the processor in the house can anticipate by one or two second and be there waiting for it. The two can fall into lock step. Is the processor in the house going to have a lot to do besides waiting for the weather packets?
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Tracy Allen
www.emesystems.com
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- Stephen