I have been playing with the DSO-138 Oscilloscope kit and the DLO-138 revised

firmware for this kit. If you don't know what the DSO-138 oscilloscope kit is then

search for it. I don't plan to publish the hardware design changes or firmware changes

that I have made. I will give a summary of the changes and if you are interested email

me and I will make the details and source code available to you.

Here is a summary of the changes that I have made:

Fully implemented the second analog channel including display of the gain and

mode (GND, AC, DC) just like the first channel.

Added a display of the selected trigger voltage

Added a control to switch the trace information display (frequency, peak, min, average

voltages, etc) to either analog channels.

Improved the selection of which channels are displayed. Now I can select any (or all) of

the channels to be displayed.

Added a flashing T to the display when it is triggered. Previously it was a flashing LED,

but my new housing makes that impractical.

Added a switch to trigger from analog channel 1 (A1) or digital channel 1 (D1).

Added a control (long press of SEL) to reverse the direction of the perimeter menu. It

was frustrating to step around to get to the control that I wanted and step one item too

far. I had to go all the way around again. A long press of SEL reverse the direction. An

arrow appears in the lower right of the display showing the current direction of step.

Implemented a selectable ALL DIGITAL mode that shows the two analog channels as digital.

This does not improve performance in any way. It just changes the display to show any

signal greater than 2V as a HIGH and any less than 2V as a ZERO. Everything related

to the analog signals (trigger, data display, etc.) still works. The change is at the point

of display. This cleans up the display and makes four digital traces clearly visible on

the small display.

Added a front end on the two digital channels to limit the input to 5.1V. The

processor pins are 5V tolerant, but I wanted to be sure it would not do damage if the

channel were accidentally connected to a high voltage. I also added a voltage follower

to the digital channels to increase the impedance. It seemed to load the circuit under

test and this fixes that.

Made the grid a little more visible and changed some color selections to make

some data easier to see.

If you would like further information and a copy of the firmware email: