Data Logger Deluxe Version Almost Done

Just to let you know the deluxe version of the data logger is almost done. The hardware is ready and tested – currently I finish the menu based software for the data logger.

  • Menu based control with 5 capacitive inputs
  • Record, view records, send records to serial, erase all, settings.
  • Wireless charging.

Compact Text Based Driver for Sharp Display

Update 2015-09-10: I also added a timer 2 based version of the driver which does not need any manual refresh.

I created a fast and compact driver for the Sharp memory display LS013B4DN04. The driver is text based and uses 8×8 pixel characters on the screen. The screen can display 12×12 characters using this size of characters.


This demo is an example of the Arduino library.


  • Uses only 174 bytes of dynamic memory.
  • Refreshes only changed rows on the screen.
    This speeds up the refresh process and makes the refresh method suitable to call it from an interrupt.
  • Each character on the screen can be displayed normal or inverted. Ideal to mark a row in a menu.
  • Fonts can provide up to 128 characters. The font can be changed at any time.
  • Minimal but complete API with direct character access, cursor based write methods and scrolling of the display in four directions.
  • Open Source

The Sharp memory display driver with manual refresh.

The Sharp memory display driver with timer 2 based refresh.

More Features Added To “Font To Byte” App

While working on the display driver for the Sharp display, I found some missing features in my “Font to Byte” application. I added this features and released a new version.

  • All bits can be inverted.
  • There is an option to print the converted characters into a useful code chart.

Driver Progress

A first version of the driver is running. It requires only ~160 bytes RAM to run. You can change the font easily, use up to 128 characters and invert any portion of the screen (e.g. for selections).

New Character Map

After converting the font into bytes, you can click the “Print Character Map…” button to generate a nice character map for your font.

New Character Map Button

This is especially useful if you added some special character. With the map you can easily lookup the correct values for the characters.

You can also save the character map as PDF from the print dialog and use the PDF as reference.

Continue reading More Features Added To “Font To Byte” App

Convert Bitmap Fonts for LCD Displays with Style

Update 2015-09-05: Added a example font and Adobe Photoshop template.

Currently I am working on the deluxe version of the data logger. This version has a LCD screen and capacitive buttons to control the software. The Adafruit library for the display is quite large and almost uses the whole RAM, because it is a pixel oriented library. My own implementation is a text only library using 8×8 pixel characters. This simplify everything and reduces the RAM costs.


To convert the bitmap font into bytes, I wrote a small application for OS X (minimum version 10.10). It accepts a PNG image with the characters in it and converts it into bytes with the correct bits set.

FontToBytes Screen 1

First you select the mode on the left side of the application window. In this example the mode is set to “8×8 Fixed Top-Down”. Select the output format in the bottom left corner of the window.

Now drag your font file onto the area on the right side. If the dragged file is accepted, the window turns blue.

Continue reading Convert Bitmap Fonts for LCD Displays with Style

Data Logger – Sensor Limits

After fixing the timing problem with the sensor library, I started the data logger and recorded data in 10 seconds intervals until the memory was full. This time the AM2302 (DHT22) sensor was read every time, no cached values were used.

It created a really interesting data set you can see in the diagram below (click on the diagram to see all details):

Data Logger Chart Fixed

The actual measured data values are the small dots in the background, and the lines are polynomial interpolated over these values.

For the temperature (blue) you can see the sensor precision limit of 0.1 and an interesting jitter when the value makes the transition from one value to another. In contrast, the humidity values (orange) do not have the same jitter like the temperature values, but you can see something strange at the crossing point of the two series.

In Detail

I created a new diagram where you can see this point in detail:

Data Logger Sensor Problems

The jitter of the humidity values is minimal, but suddenly there are huge jumps of the values. Compare the jumps with the corresponding temperature values. Because the humidity value depends on the temperature, the jitter from the temperature causes the humidity values to jump.


The test was successful: There is now real sensor data for each measurement.

If this sensor is used for a real time display of humidity and temperature values, there has to be some integrated interpolation to flatten the jitter of the read values. This is no big deal for the data logger, because you can easily do all the corrections and interpolations afterwards.

Related Files

You can download the CSV file with the measurements and the Excel sheet I used with the links below: