LEAP#188 read/write AT24C02 external EEPROM
The AT24C02 is from Atmel's line of serial EEPROM chips with a whopping capacity of 2K! (256 x 8) That's not a whole lot more than the onboard EEPROM in an Arduino, but it does have the advantage of being external:
- it can stay in-situ even if the microcontroller disappears/gets exchanged
- multiple devices can share access
As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.
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LEAP#187 nRF24L01+ Ping Pong
So now I have my nRF24 breakout boards back from OSH Park, time to try them out.
This is a simple script that runs on two Arduinos. They bounce messages back and forth over 2.4GHz using the nRF24L01+ modules, flashing their LEDs when messages successfully handled. Sweet, and the breakout boards work just fine.
As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.
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LEAP#176 nRF24 Breakout Board
So recently I've been intrigued by small-batch PCB fab services, like OSH Park. Like the ready supply of components from various online sellers, it's amazing how cheap you can get boards made over the net these days. How do they do it? As I learned in this hardware hangout, there are some neat tricks done behind the scenes to aggregate small orders into full panels sent to a fab.
But to get PCBs made, you need to be able to drive an EDA tool like KiCad. KiCad's a beautiful open source tool, but it is quite idiosyncratic. In some spare time, I dived into the KiCad like a Pro course and found it an excellent leg-up on the process.
The nRF24 breakout board (below) is just the first trivial exercise from the course. But it will come in handy - I have a batch of nRF24's lying around that I've been planning to experiment with, and the breakout board will be quite handy for that.
I just received my boards from OSH Park (1 month from order to delivery in Singapore - not bad, especially for $4.80 all-in). Very impressed with the board quality. Not so much with the board design! A few things I can see could be easily improved, but that's my fault (see my notes). But they do work!
As always, all notes, schematics and code (including the KiCad project) are in the Little Arduino Projects repo on GitHub.
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LEAP#186 Asynchronous Counters with JK Flip-Flops
A quick demonstration using four JK flip-flops set up in "toggle" mode to implement an asynchronous 4-bit binary counter. This is the classic circuit, straight out of a text book. It's implemented with:
- two 74LS73 for the flip-flops
- a 555 Timer astable oscillator providing the clock pulse
Why "asynchronous"? This refers to the fact that the output of each flip-flip cascades to trigger the next in series. Although instantaneous to the eye, there is none-the-less a propagation delay as the changes ripple through the flip flops. It's clearly seen in an analog scope trace. Here is the falling edge of 0xF transitioning to 0x0, which ripples over about a 42ns period:
Here's a quick video of the circuit in action ... though definitely not the most exciting thing you'll see on YouTube today:
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