For those who’re designing a circuit involving something from a microcontroller or an FPGA to a classic CPU, you’re going to wish a clock supply with the correct frequency. The vary of frequencies wanted varies considerably, so that you’ll should have lots of choices available if you wish to be ready for something. For a lot of electronics fans, meaning having a couple of drawers of their element organizer loaded with a collection of oscillators.
In fact, you possibly can’t have an oscillator available for each risk — at the least not with discrete parts. However with David Johnson-Davies’ Digital Sign Generator , a single piece of {hardware} can cowl all the things from 2 Hz all the way in which as much as 33.5 MHz. And I do imply all the things — the Digital Sign Generator could be adjusted in tiny increments.
Reasonably than counting on typical timer {hardware} that divides a clock by completely different values, Johnson-Davies takes benefit of the Numerically Managed Oscillator (NCO) mode discovered within the timer/counter peripheral of Microchip Expertise’s AVR EB-series microcontrollers. This strategy produces evenly spaced frequency steps throughout all the working vary, making it attainable to dial in an actual output frequency as a substitute of settling for the closest obtainable possibility.
The venture is constructed round an AVR16EB28 microcontroller paired with a 4.194304 MHz crystal oscillator for improved accuracy over the chip’s inside clock. A built-in phase-locked loop (PLL) multiplies that frequency earlier than feeding it into the NCO, permitting the generator to provide crystal-accurate sq. waves from 2 Hz to roughly 33.5 MHz. Higher but, each frequency is accessible in 2 Hz increments, giving the system a formidable stage of flexibility for such easy {hardware}.
An built-in numeric keypad permits an actual frequency to be entered instantly, and a rotary encoder supplies fast positive changes. The chosen frequency is displayed on a small 128×32 OLED, and the sign is accessible on two output pins that produce complementary sq. waves. The venture documentation additionally discusses various working modes, together with configurations that commerce frequency decision for an excellent larger most output frequency.
Whereas the NCO structure does introduce a small quantity of timing jitter at sure frequencies, the common output frequency stays extremely correct. In keeping with Johnson-Davies, this impact turns into proportionally insignificant because the frequency will increase.
For anybody who commonly works with digital electronics, this could possibly be a really helpful bench device. Whether or not you are citing a brand new FPGA design, experimenting with retro processors, or testing counters and logic chips, having almost each frequency from 2 Hz to 33.5 MHz obtainable from a single system is much more handy than sustaining an enormous assortment of particular person oscillators.The Digital Sign Generator (📷: David Johnson-Davies)
The circuit diagram (📷: David Johnson-Davies)
Waveforms generated by the system (📷: David Johnson-Davies)