So, now I want to know how to reuse an old calculator keypad in an electronics project. Any info on the Internet? Well, that’s a tough one.
I found this interesting article about calculator versus telephone keypads on the Internet.
20181107/DuckDuckGo reuse old calculator keypad
20181107/http://www.todayifoundout.com/index.php/2015/10/keypad-numbering-different-phones/
You can try buying a calculator keypad off of Alibaba. No thanks, that kind of defeats the purpose of being able to reuse.
20181107/https://www.alibaba.com/showroom/calculator-keypads.html
Here’s an Arduino project on building a calculator using a calculator keypad, an LCD screen, and an Arduino.
20181107/https://www.instructables.com/id/Arduino-Calculator/
Here’s the keypad used, available on Digikey.
20181107/https://www.digikey.com/product-detail/en/96BB2-056-R/GH5011-ND/12622
The datasheet for the keypad. Indeed, it is a simply matrix key scan system.
20181107/https://media.digikey.com/pdf/Data%20Sheets/Grayhill%20PDFs/96%20Series.pdf
Now, I’m trying to understand key ghosting. Why is diode isolation required to prevent key ghosting? It can be explained like this. With just a matrix of wires, currents can flow in any direction. In the principle use case, you only want current to flow through one side of the matrix, to a key, then flow to the other side of the matrix. If only one or two keys are pressed, this is guaranteed to always be the case when scanning the keyboard. But if three or more keys are pressed, then it is possible for current to travel a backwards path through one of the keys, turn around at a second pressed key, then flow to the other side, effectively registering a current path that would be decoded as the ghost key. To prevent ghost keys without diode isolation, the keyboard controller can do “jamming” by signaling an error instead of scan codes if more than two keys are simultaneously pressed. By contrast, if you want to simultaneously detect more key presses are are willing to pay extra money to do so, you can add in the diode isolation, which conversely simplifies the controller as it does not need to check for key jamming.
The blue arrows in the diagram indicate the travel of electric current from the GPIO output connected on the columns to the GPIO input connected on the rows. The green circles indicate the pressed keys. The red circle indicates the ghost key.
20181107/https://en.wikipedia.org/wiki/Rollover_(key)#Ghosting
20181107/https://en.wikipedia.org/wiki/Keyboard_matrix_circuit
Calculator LCD display = multiplexed display.
20181107/https://en.wikipedia.org/wiki/Rollover_(key)#Ghosting https://en.wikipedia.org/wiki/Multiplexed_display#Character-oriented_displays
This is an interesting method to combine I/O pins for both scanning an LCD display and scanning a keypad.
20181107/http://ww1.microchip.com/downloads/en/appnotes/00529e.pdf
So, you’re wondering how to cut circuit traces on a printed circuit board? What is the best way to do this? Here’s how. First, you use a surgical knife, micro drill system, or razor blade to cut the trace. Next, the best practice is to seal the gap between the cut trace using epoxy. Note, however, that you’ve also got to be sure that the traces you desire to cut are not within an inner layer of the circuit board. So long as the traces can be cut on one of the outer-most layers of the circuit board, you’re good.
Printed circuit boards are interesting in their strengths and weaknesses. One of their main weaknesses is that they are not easy to modify. On the other hand, one of their strengths is that they are very easy and cheap to manufacture, so if you do need to make modifications, simply print a new PCB. But, in light of this, one of printed circuit boards weaknesses is that their manufacturing process is not very friendly to our planet and our living environments. This problem is compounded with the increased waste of manufacturing new printed circuit boards and throwing away old ones every time changes are made to a design, especially if we’re talking about designed commercialized in the consumer mass market.
20181107/modify printed circuit board
20181107/http://circuits-central.com/pros-cons-printed-circuit-boards/
This is a really great site all about the subject of modifying advanced electronics circuit boards and the like. Indeed, it does contain information on how to cut traces on a circuit board.
20181107/http://www.circuitrework.com/guides/guides.html
20181107/http://www.circuitrework.com/guides/4-3-1.html