arduino | Assorted small Arduino hacks

Raster or bitmap fonts are represented in a number of different ways and there are bitmap font file standards that have been developed for both Linux and Windows. However raw data representation of bitmap fonts in programming language source code seems to vary depending on:

• the memory architecture of the target computer,
• the architecture and communication pathways to the display controller,
• character glyph height and width in pixels and
• the amount of memory for bitmap storage and what measures are taken to make that as small as possible.

A brief overview of bitmap fonts

A generic bitmap is a block of data in which individual bits are used to indicate a state of either on or off. One use of a bitmap is to store image data. Character glyphs can be created and stored as a collection of images, one for each character in the character set, so using a bitmap to encode and store each character image is a natural fit.

Bitmap fonts are bitmaps used to indicate how to display or print characters by turning on or off pixels or printing or not printing dots on a page. See Wikipedia Bitmap fonts

A bitmap font is one that stores each glyph as an array of pixels (that is, a bitmap). It is less commonly known as a raster font or a pixel font. Bitmap fonts are simply collections of raster images of glyphs. For each variant of the font, there is a complete set of glyph images, with each set containing an image for each character. For example, if a font has three sizes, and any combination of bold and italic, then there must be 12 complete sets of images.

A brief history of using bitmap fonts

The earliest user interface terminals such as teletype terminals used dot matrix printer mechanisms to print on rolls of paper. With the development of Cathode Ray Tube terminals bitmap fonts were readily transferable to that technology as dots of luminescence turned on and off by a scanning electron gun.

Earliest bitmap fonts were of a fixed height and width with the bitmap acting as a kind of stamp or pattern to print characters on the output medium, paper or display tube, with a fixed line height and a fixed line width such as the 80 columns and 24 lines of the DEC VT-100 terminal.

With increasing processing power, a more sophisticated typographical approach became available with vector fonts used to improve displayed text quality and provide improved scaling while also reducing memory required to describe the character glyphs.

In addition, while a matrix of dots or pixels worked fairly well for languages such as English, written languages with complex glyph forms were poorly served by bitmap fonts.

Representation of bitmap fonts in source code

There are a number of bitmap font file formats which provide a way to represent a bitmap font in a device independent description. For an example see Wikipedia topic - Glyph Bitmap Distribution Format

The Glyph Bitmap Distribution Format (BDF) by Adobe is a file format for storing bitmap fonts. The content takes the form of a text file intended to be human- and computer-readable. BDF is typically used in Unix X Window environments. It has largely been replaced by the PCF font format which is somewhat more efficient, and by scalable fonts such as OpenType and TrueType fonts.

Other bitmap standards such as XBM, Wikipedia topic - X BitMap, or XPM, Wikipedia topic - X PixMap, are source code components that describe bitmaps however many of these are not meant for bitmap fonts specifically but rather other graphical images such as icons, cursors, etc.

As bitmap fonts are an older format many times bitmap fonts are wrapped within another font standard such as TrueType in order to be compatible with the standard font subsystems of modern operating systems such as Linux and Windows.

However embedded systems that are running on the bare metal or using an RTOS will normally need the raw bitmap character image data in the form similar to the XBM format. See Encyclopedia of Graphics File Formats which has this example:

Following is an example of a 16x16 bitmap stored using both its X10 and X11 variations. Note that each array contains exactly the same data, but is stored using different data word types:

Looking at the code of the circular buffer:

You have to first find whether the request is coming from arduino or andriod.

To make that happen, if it is GET method from client side you have to pass something like,

app=arduino or app=android in query params.

If it is a POST method you can send in request body(app: "arduino").

So in Django views, can declare some list like,

UN_AUTHENTICATED_METHODS = ['get_users']

get_users is a method

After that in your function,

Before explaining, you have to understand a few things:

• Characters (i.e., a char type) can be treated as a number without any cast based upon its ASCII encoding
• Strings in C always end with a NUL terminator. Importantly, this character has a numerical value of 0 (i.e., when you treat it as a number, it's equal to zero).
• Boolean values don't really exist in C independant of an integer representation. Zero is treated as "false" and anything else is treated as "true".

With this out of the way, let's look at what's happening in the loop.

First, we have a pointer p that points at the first character of the string "Hello world!\n" (this is coming from the statement const char* p = "Hello, world!\n").

At the top of the loop, we check our loop condition, which is c = *p. Note that this assigns the value pointed at by p into c, and assignments in C evaluate to the value that's been assigned. What that means in this context is that our test is essentially just *p.

Since booleans don't exist in C, *p is false only when the character pointed at by p has a value of zero. This can only happen when p is pointing to a NUL terminator, which is always at the end of a string in C. Therefore, our loop will stop when we've hit the end of our string.

Since you have the value returned by the Arduino in a variable, you can use it in your If statement:

After return ; or just return; (for void functions) the program exits from the loop and also from function. The function returns (for non-void functions). This statement applies when executing function already is not requeris.

It seems to me that the problem solved.

I have managed to replace the String buffer with a char one in external memory. It seems stable but requires more testing. I'll post the solution but if anyone has a better approach feel free to comment here.

Thanks.

Add this to a .htaccess file created in the directory you save the .txt files:

The compiler error says:

the trait bound &mut T: avr_hal_generic::embedded_hal::adc::Channel is not satisfied

Notice that the error is asking for &mut T to implement Channel, &mut T: Channel<...>, whereas your T has the bound T: Channel<...> — applying to T itself rather than &mut T. That's why the bound you've already written isn't helping.

Now, what's the right fix? If I look at the docs you linked, I can find the type of ::read. (Note: I copied the text from the docs to construct this snippet; I didn't read the source code.)