Over the years I have often taken a oscilloscope displaying logo's and text using the x y mode to events my Makerspace has been helping at. Normally driving it using the PWM pins on a Ardiuno and a RC circuit to smooth out the jitter.
A couple of years ago i came across an excellent youtube video by Alan Wolke, in which he used a R2R ladder as DAC this improved refresh speed and overall enabled the display of a more detailed image. He later improved on this using code from Bob at VintageTek. I have included links to both these invaluable youtube videos below.
Step 1: Schematic
The circuit is pretty much a direct copy of Alan Wolke's but I opted to just a R2R array as apposed to making it out of individual resistors. This was largely due to laziness and not wanting to solder all those resistors in!
Step 2: Prototype
Quickly after seeing the video I upgrade my solutions using a protoboard shield. This served us well and was used at many events but whilst it worked it was a little fragile, So I decided to make life easier and build a PCB version of the shield. This would make It simpler to set up and improve reliability.
Step 3: PCB
To be honest designing a PCB was probably overkill, and I did so not least as a learning experience. I opted to go with BNC connectors as they are simple and always at hand. If you opted for just connecting probes directly you should be able to omit the capacitors as the probes should have enough capacitance themselves.
Step 4: Parts & Assembley
The following is a list of parts you will require to build the shield.
- 2 x AMP 5227161-1 BNC Coaxial, Right Angle Jack, Through Hole Right Angle, 50 ohm Connectors
- 2 x BOURNS R2R 10 kohm, SIP, Bussed, 4300R Series, 10 Pins Resistors
- 2 x KEMET C317C100J1G5TA Multilayer Ceramic Capacitor, Gold Max, 10 pF, Goldmax, 300 Series
- 0.1 pitch Pin Header
You will also require solder and maybe flux to assemble.
To use it you will need
- Arduino (I used an Uno)
- 2 x 50ohm BNC to BNC cables
- Oscilloscope with X Y Mode
Step 5: Code
Rather than reinvent the wheel I have used the code suggested on Alan's youtube post. It really does a very good job! You can download it here. http://www.qsl.net/w2aew/code/logor2r.ino
I have since created a few extra displays.
Step 6: Examples
A couple examples of the type of things you could display on your scope. Animation is also possible but I have not yet tried this.
Step 7: Conclusion
In conclusion a nice fun little project. I have plans on how i might adapt this going forward but going to keep this a secret for now.
Still not sure I got the correct value for the capacitors if I get chance I might try a few other values.