Build an AM Radio Transmitter from a CPLD

[Alex Lao] has been playing around with the CPLD-like parts of a PSoC. Which is to say, he’s been implementing simple logic functions “in hardware” in software. And after getting started with the chip by getting accustomed to the different clock sources, he built a simple AM radio that transmits at 24 MHz.

The device that [Alex] is learning on is a Cypress PSoC 5LP, or more specifically their (cheap) prototyping kit for the part. The chip itself is an ARM microprocessor core with a CPLD and some analog tidbits onboard to make interfacing the micro with the outside world a lot easier. [Alex] doesn’t even mess around with the microprocessor, he’s interested in learning the CPLD side of things.

PRS-CircuitHe starts off with a 24 MHz carrier and a 1 kHz tone signal, and combines them with a logical AND function. When the tone is on, the carrier plays through; that’s AM radio at its most elemental. Everything is logic (square waves) so it’s a messy radio signal, but it’ll get the job done.

Adding a multiplexer up front allows [Alex] to play two tones over his “radio” station. Not bad for some simple logic, and a fantastic Hello World project for a CPLD. We can’t wait to see what [Alex] is up to next!

If you’re interested in getting your feet wet with either CPLDs in general or a CPLD + micro system like Cypress’s, the development kit that [Alex] is using looks like a cheap and painless way to start. (Relatively speaking — PSoCs are a step or two up a steep learning curve from the simpler 8-bit micros or an Arduino.) Hackaday’s own [Bil Herd] has a video on getting started with another member of the Cypres PSoC family, so you should also check that out.

Video: Getting Your Feet Wet with Programmable System On Chip

Ever since I received my PSOC 4 Pioneer kit from Cypress I have wanted to play with this little mixed-signal Programmable System-on-Chip (PSOC) developer board. I love developer boards, providing that they are priced in a way to entice me to not only open my wallet but also make time in a busy schedule. I think my kit was free after winning a swag bag from Adafruit that they themselves obtained at the Open Hardware Summit and gave away on their weekly streamcast. Ultimately it was the invitation to beta test which also was included in that pile of swag that led to my getting involved with Hackaday.

What is Programmable System On Chip?

So what is a PSOC 4? A quick summary is that it’s based on an ARM Cortex reduced instruction set processor (RISC) and is somewhat capable of supporting shields based on the Arduino footprint, and it also uses a bright red PCB that I have come to associate with a Sparkfun PCB. What doesn’t show is the fact that this programmable system on chip has programmable analog function blocks in addition to programmable digital logic blocks. There is also some supporting input/output circuitry such as a multicolored LED and a capacitive touch sensor directly on the PCB.

Pioneer 4 Development Kit
PSCO4 Development Board on Hackaday

This is an intriguing amount of programmability, so much so that Newark/Element 14 highlighted a “100 projects in 100 days” event on it.

Enter the IDE

Over the years I have had to create or install many Integrated Development Environments (IDE) that linked hardware to software. Knowing that you had to, and how to, implement an IDE was part of being an engineer. Nowadays with the Arduino type environment the user has an IDE pretty much as soon as they click on the executable which I find to be one of the best aspects of the genre. It was so quick in fact that I was able to get my teenaged son into writing his first program even before he remembered to do massive eye-rolls and make sounds of utter disdain. He did give up however, just shy of learning how to have the Arduino make sounds of disdain on his behalf.

PSCo4 Cypress Development Kit on Hackaday
Closeup of a Programmable System on Chip Development System

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Re:load Pro, an Open Source Active Load

Open source test equipment has to be one of the best gifts open source hardware has given back to the community. Nowhere is this more true than in the case of  [Nick’s] Re:Load Pro over on Kickstarter. Unlike resistors or similar dummy loads, an active load will always draw the set amount of current regardless of voltage. Active loads are often used to test power supplies and batteries. Is that 2500 mAh LiPo battery overstating it’s capacity? Can the power supply you just designed handle 2.5A at 12V? Both of these are jobs where active loads would come in handy.

The Re:Load Pro is actually the third version of the Re:Load. [Nick] designed the original Re:Load after becoming frustrated at the lack of a cheap active load for testing a power supply. Plenty of people showed interest in the Re:Load, but they wanted more features. That’s where the Re:Load Pro comes in. More than a straight analog design, the Pro has a Cypress PSOC 4 Arm Cortex M0 processor running the system.

[Nick] and his company, Arachnid Labs, are no strangers to us here at Hackaday. When we last covered [Nick], he was asking the USB Implementers Forum about a low cost Vendor ID option for open source hardware projects. Fittingly, the Re:Load Pro is an open source project. The schematics and source code are available on Github.

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