Odds and Sods

Haven’t had much time to do anything too interesting lately, sorting out my garage has been more important. I did get around to 555 PWM timer stuff though and that worked out OK. It’s always useful to have a reason to do something and, in this case, it was to provide a fan speed controller for my mate Chris and his 50W LED uplighter project.

I didn’t use the circuit I’d found previously, a bit more digging on Google led me to a tutorial on the Dallas Personal Robotics Group site. They provide a really good write up and there’s no point me repeating any of it. Their schematic is:

DPRG Schematic

That’s pretty much what I put together and here it is on test:

555 PWM Board (lower left)

555 PWM Board (lower left)

The LED driver outputs about 36V so I had to knock up a DC buck converter to drop that to 12V for the 555 circuit and the fan. I have a few LM2575-ADJ switching regulators that I picked up from eBay a while ago so I used one of those with the circuit straight out of the datasheet:

LM2575-ADJ, from datasheet

LM2575-ADJ, from datasheet

It seems to work well and it should be just a case of setting the pot to a sensible value that will both allow the fan to startup and not sound like a jet engine.

This also seemed like a good opportunity to dig out my “entry level” JYE Tech DIY Oscilloscope to see if I could get anything useful out of it. I was aiming for a frequency of around 30kHz so C1 is chosen as 470pF. What did I achieve?

Actual frequency (Hz)

Actual frequency (Hz)

Not quite! That should still be a high enough frequency not to annoy older ears though. Here are a couple of waveform shots:

"Sort of"  Square Wave

“Sort of” Square Wave

Zoomed in

Zoomed in

That’s much “squarer” than I expected. Can’t see that the fan’s going to mind much! So, that’s done, I’m sure I’ll find out how well this works at some point.

While I had all my stuff out, I decided to modify a few of the really cheap 5V output DC boost converters I’ve been picking up from AliExpress. They’re fine (and you can’t make anything like them for anywhere near the price) but come with a USB “A” female output connector:

Blurry picture

Blurry picture

They’re pretty handy and will chuck out 5V quite happily from a couple of AA batteries – I’ve found them useful to generate 5V to power 1W LEDs placed in cupboards for instance.

I’ve always thought that they would be more useful if the USB connector was, er, optional. And it is 🙂 – well, if you hack it off with your snips and solder wires on instead…

Slightly modified 5V boost converters

Slightly modified 5V boost converters

It’s useful to have a few around in that format. Luckily the chunky corner pads for the USB connector aren’t connected to anything (I expected them to be grounded) so they make for great strain relief.

I’m currently waiting for some 3V3 boost converters from CISECO which are about £5 each! Haven’t found any equivalent from AliExpress and, even at £5, I still can’t buy the bits and make my own any cheaper. I was going to buy a surface mount radio module from CISECO and design a circuit board to use some of my pile of ATmega328 chips but, again, it was much cheaper and easier to just buy their RFu-328 product which ticks all the boxes. Looking forward to those turning up then I can start to unleash wireless sensors all around the house, in the loft, in the garage, whatever. I’ll start small though… and I do need one to control some Xmas lights that I’m planning for the porch (controller and PSU will have to be in the loft).

Onwards and, er, whatever…

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