square wave

ATtiny85: Blinking Without Clock Cycles


In the previous post we learned how to blink an LED with an ATtiny85 by using a _delay_ms() function to halt the program execution after turning on and off the LED. The downside to this approach is that the _delay_ms() causes our code to hang up while the function spins in a loop up to the specified time. This is a waste of CPU clock cycles, and makes doing anything else in the event loop nearly impossible. Let’s stop the pointless spinning.

In this post I will introduce the two timer/counter hardware peripherals that are inside the ATtiny85 chip, and show how we can offload the job of blinking an LED to one of them with the added benefit of using no clock cycles on the task. This frees the CPU up to do whatever else we wish while our LED reliably blinks away. If you are coming from a typical Arduino upbringing, this sort of flexibility and power is what makes learning how to truly program a microcontroller and its peripherals worth the effort.
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Square Wave Generator and PWM with a Numato Elbert v2 FPGA

Last time we outlined how to divide down an FPGAs clock frequency using a basic counter circuit. This allowed us to have varying blinking frequencies for our LEDs depending on which bits of the counter register we tied them to.

What if we needed to adjust for a specific frequency of blinking, of wanted to adjust the time the LED is on vs off? What we are looking for is a programmable square wave generator. I will show you how we can program an FPGA in Verilog to act as one that takes two 4-bit inputs to control the on/off periods of the square wave.

Once we have went through the process of adjusting the on/off timing of a square wave, creating an adjustable PWM output for an LED comes naturally. We will see how to program an FPGA to output a PWM signal that allows us to adjust the brightness of an LED based on a 4 bit input signal.

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