2.0 Discussion: Units, sensor types and protocol

[Yveaux]

@hek said:

V_DIRECTION

Maybe just return angle ( in radians and call it V_ANGLE) then textual indication. This way higher resolutions can also be supported.

Sorry for all the separate messages. Works more convenient on a tablet...

[Yveaux]

I would like a way to configure a sensor from the gateway, to e.g calibrate a sensor or store some ID. Maybe a V_CONFIG can be added, where childid indicates the actual variable written. Or define a few V_CONFIG0,V_CONFIG1 etc.
What do you think?

[hek]

@Yveaux said:

g/m3 if you standardize on SI
Same for distance BTW. Might be more...

I choose to scale the SI units to something relevant for thing getting measured. E.g. g/m3 would give a VERY small small value for dust.

Distance is mainly for the distance sensor now, which only has a small range.

Rain - measure in meters would also render very small numbers.

So, until we have a scaling factor in the protocol or something similar we'll have select a proper scaling at the source and agree on it between sensor and controller.

[hek]

@Yveaux said:

V_CONFIG0,V_CONFIG1

A few config-placeholders would be a nice.

[hek]

@gregl said:

V_PH_LEVEL

Added.

[hek]

@Yveaux said:

Why average/highest over last hour? My weather station reports wind speed every minute and I like to see the minute detail instead of averaging everything over an hour.

I'll change the definition to "over the last report period".

[a-lurker]

V_ANGLE sounds good. With a bit of (floating point) maths, all can be calculated.

[hek]

@ServiceXp said:

V_RELAY_STATUS 1=Active, 0=Deactive

Not sure what differs this form V_LIGHT_STATUS.
Maybe we need a better word than LIGHT that describes a thing-that-can-be-turned-on-or-off?

[Yveaux]

@hek said:

So, until we have a scaling factor in the protocol or something similar we'll have select a proper scaling at the source and agree on it between sensor and controller.

When values are sent as floats it doesn't matter. Scaling is implicitly store in the floating point value when sent as binary float. When transfered as ASCII you're right, but that isn't required with 1.4 anymore...

[Yveaux]

@hek said:

a thing-that-can-be-turned-on-or-of

Hmmmm.... Let me think.... a switch ? ;-)

[hek]

@a-lurker said:

Electrical impedance and resistance are not the same thing- suspect resistance is intended here?
V_IMPEDANCE --> V_RESISTANCE

I think the impedance-variable comes from the RFXTRX plugin. And it is related to body fat measurements for body scales.

http://code.mios.com/trac/mios_rfxtrx/browser/trunk/L_RFXtrx.lua

If I understand it correctly Impedace is used for AC and resistance for DC. Not sure what would be most useful in this setup.

[hek]

@Yveaux said:

When transfered as ASCII you're right, but that isn't required with 1.4 anymore.

Most users still use the serial protocol. Which means strings like "0.000003423" must be generated and transferred to the controller from gateway.

[hek]

@Yveaux said:

Hmmmm.... Let me think.... a switch ?

Haha.. yeah.. :+1:

[Damme]

@hek Moisture or Water detecded... Might be 2 different ?
Thinking different applications: Moisture in ground. (I.e. Water needed? Ground dry?) And Water level, hmm, if you have a fluid level meter to detect overfill. or leakage. Fluid flow

[Yveaux]

@hek said:

strings like "0.000003423" must be generated and transferred

Ok, but is this a problem? You could even pass it as 3.423e-6....
You don't want this string on air if you can transfer the same thing in 4 bytes, that's true.
I only want to state that if you transfer it purely in SI units, without scaling, you always know what the actual value is.

[Yveaux]

I'm still in doubt if we really need all these different value types...
In principle a (light) switch, water level sensor, burglar alarm, heater status <fill in your own binary switch> all just return or take 0 or 1. V_BINARY should suffice for all of them.
For other values you see the struggle between defining them as bare units (V_AMPS, V_VOLTS, V_CUBIC_MEASURE) and function (V_FLOW, V_WEIGHT, V_HUMIDITY).
Can't we just live with transfering values by specifying their units only and leave the interpretation of it to the controller (e.g. V_AMPS, V_BINARY, V_PERCENTAGE) ?
I'm not familiar with Vera, but e.g. the OpenHAB/MQTT combination doesn't care at all what type of value is exchanged. It's up to the configuration of OpenHAB how a value is interpreted.

[hek]

@Damme said:

Moisture or Water detecded... Might be 2 different ?

For water detected I would probably use V_TRIPPED.

Hmm.. Soil Moisture.. I have no idea how to represent this. Help me! The ebay sensors we're using isn't super accurate and comes uncalibrated.

[Damme]

@hek I know, ist more 'need moisture' or not :) Hmm... V_Moisture, (relative) 0-255 / 0-100% / True | False

[Yveaux]

@hek Can we also pass battery level as just a sensor value? There's no real need to pass this as an internal message, is it?

[Zeph]

First off, this is a very positive step forward!

Now some details
@hek said:
> I think the impedance-variable comes from the RFXTRX plugin. And it is related to body fat measurements for body scales.

I think that we need to be clear about the core concept of what we intend to measure.

Resistance or impedance generally don't make much sense, as they are usually not the conceptual thing being measured but an intermediate value used in calculating it.

This is also true of Volts and Amps, except that sometimes we really do want volts and amps (for power monitoring).

But consider a Light Dependent Resistor in a bridge circuit.
We could report the value as ADC readings 0..1023.
Or we could convert that to volts 0..3.3 or 0..5.0 or whatever.
Or we could convert that to LDR resistance (knowing the other resistor value) in ohms.
Or we could do some calcs and try to report the result in Lux.

Since the conceptual thing we are trying to measure is light intensity, the best option would be to report it in Lux if possible. Not as ohms, volts, or ADC readings.

So any time we see something reporting as resistance or impedance, we should ask if that's the core concept we need to report, or an incompletely processed proxy that will be hard for the server to understand.

Likewise with volts or amps - are we really trying to report temperature or humidty or what? If we are monitoring a battery or the AC mains, then maybe volts it exactly right, but we need to think it out first.

So who in a home automation context cares about resistance or impedance as the core thing being measured?