What you are watching in the video:
Fox loopback notes:
Looking at the image above of the GLCD during local loopback (sanity testing) you will notice a RED “T” at the beginning of every line. If you want to change this to any printable character, simply edit the value in the source code. For example, when using for GPS, hi lighting “$” may be useful. If you wish to disable this feature, simply use any non-printable character, such as \008.
Horizonal solid lines are lines where the cursor advanced to the first position on the line and the next character was a carriage return. Therefore, the software shows this line.
As characters are displayed, the horizontal line is “eaten away from left to right” and the line will be removed if a carriage return is received otherwise the line wraps to the next display line.
I have been using my PICAXE (Oh, My! ) QBF generator for several years. It is on perf board on the bench with a couple of male jumper wires soldered to the uC and a 9V battery and 5V 78L05 regulator… probably $5 in parts including the name-brand battery.
The serial TTL test generator is just one of those things that you do not need until you need it. Yes, loopback tests can be conducted, serial terminals on the PC can be invoked, USB to serial adapters can be configured. But, why? This article will provide a circuit using a 32U4 Pro Micro and a ILI9340 2.2" TFT color display. Together, the investment is around $15 but the display functions as a 9600/4800 serial receive terminal and the USART Tx line can be configured with a single pin-to-ground to send 9600/4800 BAUD serial data. And the Tx and Rx lines can be connected together for sanity testing! A local loopback.
You can find more video and pictures of the build here:
Also, on the above link is the source for the display and the Pro Micro but if you wish, you can purchase the display (different pinout) from Adafruit and the Pro Micro32U4 from Sparkfun. Total China costs are under $15.
But I have posted the code (ZIP) and incidental information here. This project could easily support a front-end menu for configuration defaults written to eeprom. But, switches are likely the way I will build out the permanent addition to my test bench… because I like buttons and switches. For my use, 9600 BAUD is the default and Rx only is the default mode, so no jumpers or switches needed! Ground Pro Micro pin#4 to activate the QBF Tx generator mode and Ground pin#6 to lower the BAUD to 4800. Simple.
NOTE: The Pro Micro is running at 3.3V and 16MHz. Please do not tell me this is not supported, I know that. I will say that I have run many 328p and 32U4 from 3.3 Volts without any issues. If it does not work for you, that is regrettable. I cannot guarantee what Atmel will not, but I have never had a single issue in numerous builds but these projects were tested in what would be considered room-ambient temperatures: from 62F to 78F so there were no extreme testing completed.
Please post improvements and additions/corrections to the code base.
Enjoy. This inexpensive home-brew test equipment may be as valuable to you as your DVM.
Added: If you do not understand the proper 3.3V to 5V connection issues, please review this document:
If you are just connecting the 3.3V Tx to a 5V TTL Rx, then no circuitry is required.
If you are connecting a 5V Tx to the 3.3V Rx, then you can get away (usually) with a 10K series resistor.
For long term use with 5V interfacing, the logic level converter is recommended.
QBFgenerator.zip (5.45 KB)