Pokit

Long long time without writing something, I guess I'm really busy :)
However something happens in my world.

A couple of years ago I did find an interesting Kickstarter project and I decided to participate, Pokit.

It took forever to receive finally the product but in the end, finally arrived !
Few notes about it.

fHelper - capacitive humidity sensor

Time ago I did use a traditional humidity soil sensor (from the Grove family) for the fHelper project and it ended up very badly.


After some search I decided to try a capacitive sensor.
There are many on the market, so I just did pick up one of the cheapest
and easy to have one, from Amazon.


This is a brief review of this sensor.

Radioactivity measurement - First hike of the year

Measurement done during the first hike of the year in the Flatside Wilderness area (AR).

Radioactivity measurements - Rattlesnake Ridge hike

Measurement done during a hike on the Rattlesnake Ridge area.

Radioactivity measurements - stationary test

The first measurement is a stationary test I did in the office (North Little Rock).
I left the geiger turned on for few hours in the same position.

5V Solar Power Supply for Raspberry Pi - first results

The introductory article was about describing the feasibility of the project.
Let's see some preliminary results.

The measurements

Until now I did run the system with an external voltmeter to see if the solar panel was able to keep up with the system.
It seems that so far the answer is no.

The graph shows the battery level measured in few days.
Note that basically there was no real load to the battery, only the Dc/Dc converter, so very few mA were drawn from the battery.
The days were pretty cloudy all the time, so no full sun for long time. In the best scenario (see the latest days) the battery level barely reached the 2.9V, well well below the minimum of 3.5V, and again I stress the fact there was no real load on the system.

The solar panel used so far is a 6V 2W, capable to provide in full sun a current of 330mA.
Definitively not enough to keep the battery charged AND powering something else (the Raspberry Pi has an estimated drawing current around 300-350mA).

Until there was sun the system did run happily, but as soon as the solar panel was not in full sun, the system had to use more and more the battery to power up the project and of course there was no battery charging there.

The battery is a nominal 3.7V 6600mAh and can last just few hours when not charged, so the system starting with a loaded battery in a sunny day can run almost all the day, but that only the first day.

What to do ?

There are few things to try.

1. Use a bigger and powerful solar panel.
   A bigger solar panel, still 6V but maybe 6 or 9 W, probably can give more energy even with less light.
   In full sun the power should be enough to charge the battery AND power the system.
   Adafruit has a 6V 5.6 W solar panel, capable to give up to 930 mA in full sun and presumably more juice even in less than ideal conditions.
    
2. Implement an intelligent power management
   We can assume to don't have the system running 24 hours a day.
   An external circuit (like the RPOf) can monitor the charge of the battery and shutdown the Raspberry when the battery level is below a specific threshold.
   When the battery threshold level is above a specific value the circuit can power on back the Raspberry.
3. Reduce as much as possible the Raspberry Pi current needs.
   It can be done disabling every thing not needed, like the HDMI port or the LEDs.
   Even better adopting a Raspberry Pi 3, eliminating also the need to power the USB ports (currently the USB ports are in use for the WiFi dongle).

Very probably all the solutions will be needed.

Sensor modification

To better handle the solar management, a modification is needed on the light sensor.
Currently the light sensor is based on a photoresistor.
It can indicate if there is light or dark but is not enough to determine the "quality" of the light.
In other words the value returned is not enough to determine if the light is enough to generate ppower via the solar panel or not.
To do so a better light sensor is needed.  So in the near future I'll use a solar light sensor rather than the generic light sensor.

TeirmiLab - Designing a laboratory thermometer

Sometime is necessary to "reinvent the hot water".
In a  laboratory is necessary to measure the temperature of liquids and not always are easily available the last technological gadgets or practical one.

This article describes very generally some characteristics, requirements and usage of the gadget to design, a thermometer to be used in a laboratory

Important ! This project is based on specific requirements. Is not meant to be a "universal laboratory thermometer" but rather an instrument with specific characteristics needed in a specific laboratory.
The idea is that it can become a starting base for similar lab thermometers.

So here this project trying to design and build quickly a thermometer suitable to be used in a laboratory : the TeirmiLab

Lets start with the name.
The name is invented taking the first part of the Irish translation of "thermometer" (teirmiméadar) and of course "Lab" does not need of explanation.
Why Irish ? Well, I liked the sound of the name. The beauty of globalization.

The idea is to have a versatile and flexible instrument, capable to collect temperatures with probes attached to the display unit, measuring the current temperature, the minimum one, the maximum and work optionally as data logger.

The TeirmiLab can be also connected to a network (enhanced version), adding the possibility to see the current measurement in real time over a browser and adding graphic capabilities, remote setting of the unit and so on.

On the market do exists a lot of thermometers for laboratory use, but one of the goal of the project is to create an open platform and a thus customizable one, without spending up to thousand dollars.

The precision of the TeirmiLab initially is set as the sensor used, the DS1820. 

Requirements

The TeirmiLab should be able to performs these functions (the list has no particular priority)

Basic

• minimal and intuitive user interface
• read one sensor. The sensor should be detachable to be able to change it or clean it
• display the temperature away from the sensor
• display the temperature in Celsius or Farheneit or Kelvin
• Alarm
• Capability to offset the reading locally (setup)
• Capability to set the alarm locally

Enhanced

• read more than one sensor
• display locally the min and max temperature
• data logger capability
• capability to store locally temperatures for an amount of time
• setting for the measurement interval
• setting for start and stop
• capability to transfer the log to a remote computer
• remote connection capability
• setting alarms
• offsetting a probe
• download log
• reset log
• remote display capability
• (optional) print results locally
• (optional) RFID reader for identification 

Let see more in details some requirements for the basic version/

Minimal and intuitive user interface

In a world of "apps" it is easy to forget that sometime is more important a practical approach rather than a fancy one.
The user interface of the instrument is based on a "traditional" LCD display and few push-buttons.
No fancy touch screen with nice graphics.
A lab instrument needs to be first of all simple and immediate to use and sturdy, ANYBODY should be able to use it after 5 minutes and the tools itself must be capable to work in an hostile environments (spills, dirt, etc.)

Alarm

The TeirmiLab should have the capability to generate an alarm if a specific temperature is reached.
The alarm can be visual (change color of the display for example), audio (buzzer) or web based (browser pop up).

Remote display from the sensor

The sensor should be detached from the main unit, i.e. connected via cable.
The thermometer should be placed away (inches) from the source to measure so to easily locally display the temperature on a local display

Local settings

It must be possible to set locally some functionality, like setting an alarm or setting up an offset.
So a mini keyboard with at least three pushbutton is necessary.
Alternatively is possible to use a rotary digital  encoder with a pushbutton.

Keyboard/Keypad

Here a button requirements:

• Mode
  The Mode button allows to change the state of the instrument.
  There are 4 modes :
• Run  (default mode)
  In this mode the temperature read from the sensor is displayed in real time (every second).
  If the alarm is set, the display will show the normal temperature in Green and will switch in Red when the alarm is reached.
• Measurement unit
  By default the measurement unit is in Celsius.
  Alternatively is possible to select Fahrenheit or Kelvin
  The selection of the measurement unit automatically update the current values (alarm/offset)
• Alarm Set
  In this mode is possible to enter the alarm temperature, using other two pushbutton to increment or decrement such value
• Offset Set
  Some sensors can have an offset. This mode allows to add a value to the reading to offset the sensor.
• Increment
  The Increment button (+) allows to increment a value
• Decrement
  The Decrement button (-) allows to decrement a value

Digital Rotary Encoder

The pushbutton on the encode select the mode, then rotating the encoder clockwise will increase a value. Rotating the encoder counterclockwise will decrease a value.

• Mode
  The push button  allows to change the state of the instrument.
  There are 4 modes :
• Run  (default mode)
  In this mode the temperature read from the sensor is displayed in real time (every second).
  If the alarm is set, the display will show the normal temperature in Green and will switch in Red when the alarm is reached.
• Measurement unit
  By default the measurement unit is in Celsius.
  Alternatively is possible to select Fahrenheit or Kelvin
  The selection of the measurement unit automatically update the current values (alarm/offset).
  Rotating the encoder will change the selection
• Alarm Set
  In this mode is possible to enter the alarm temperature, rotate the encoder clockwise or counterclockwise to increase and decrease the alarm temperature
• Offset Set
  Some sensors can have an offset. This mode allows to add a value to the reading to offset the sensor.
• Reset
  This option reset the TeirmiLab in a known configuration
• Unit used : Celsius
• Alarm disabled
• Alarm value = 0
• Offset = 0
• Setting
  When in a specific mode, rotating the encoder clockwise or counterclockwise will change the selection.