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Jon Clift's Blog

68 posts
jc2048

CMOS Crystal Oscillator

Posted by jc2048 Sep 8, 2021
Introduction   I'm currently looking at doing some digital audio stuff with an FPGA. Ideally, I need to be working with a clock that's a multiple of one of the common audio sample rates (48kHz, 96kHz, or 192kHz). 12.288MHz would be a good choice, being a reasonably high multiple of all of those, but it's an awkward value to generate using an FPGA's PLL: on my Lattice Brevia 2 board, with its XP2 FPGA and 50MHz oscillator, the closest I can get to 12.288MHz is out by 0.2%. The DAC p ...
jc2048

Noise: Transistor Preamp 3

Posted by jc2048 Jun 30, 2021
Introduction   About time I did some more blogging. This one will be a confused mess as I try to untangle and document some of what I've just been doing: regard it as a few 'notebook' pages rather than a coherent blog effort.   I'm still interested in transistor design and I've also been reading about noise. I've got a small number of books that help with this: Motchenbacher and Fitchen [1] is a practical, engineering approach that is old but, of course, the basics don't change even ...
jc2048

FPGAs are a Blast!

Posted by jc2048 Jun 3, 2021
About a week ago I bought myself a USB Programmer for Altera FPGAs and CPLDs. The place I bought it from also had a small, simple CPLD board based on a Max II part for sale, so I got one of those too. The pair came to around £16 and arrived the next day via ordinary letter post. It seemed worth buying the CPLD card simply in order to quickly try out the programmer and convince myself it worked, though I'm sure I can find some other uses for it.   Here's what the CPLD board loo ...
jc2048

The Art of Noise

Posted by jc2048 May 22, 2021
22nd May 2021     I've just been playing with a very simple noise generator and that's the result. The digital phosphor of the oscilloscope presents multiple traces of the waveform as though it were sketched with a pencil or crayon.   In case it's of any interest, here's the circuit:     The internet is full of variations, with either a Zener, reverse-biased LED, or reverse-biased base-emitter junction as the avalanche 'noise diode'.       For t ...
jc2048

JFET Colpitts Oscillator

Posted by jc2048 Jan 9, 2021
Introduction   This one started last year with me just messing around on a windy, rain-swept day, seeing if I could do something simple with a JFET. It's taken quite a while to make it to the blog: I dropped it, started it again, stalled, and have now, eventually, finished it. [It was also leap-frogged by the regulator-as-an-oscillator one, which you'll notice had quite a lot in common with this one.]   What I was trying for was an oscillator that had an output frequency of se ...
This one came out of reading about GaN FETs in this 'essentials' blog: Semiconductors I GaNFETs for Power Conversion   When I had a look at the datasheet for one of the parts being advertised, I realised from the equivalent circuit that it was a cascode combination of an Si [silicon] MOSFET and a GaN [gallium nitride] FET (it would appear that that combination has become available because it looks like they are growing the GaN on a Si substrate). This is how it's shown in the datash ...
jc2048

TL431 Oscillator

Posted by jc2048 Oct 3, 2020
This one isn't too serious.   When shabaz did a blog on using a TL341 as a Low Battery Warning Indicator, I wondered what else you might use the device for. Since it includes an amplifier, it shouldn't be too hard to get it to oscillate, so that's what I thought I'd have a go at. See if I can get a sinewave out of it.   As I'm just doing this for fun, I'm going to slap together the circuit without too much detailed design and see what happens. I wouldn't recommend that you actually u ...
This is a very quick item to get me going again and back into the habit of blogging.   When jancumps showed us a one-transistor current source in Simple Electronic Control Systems - Current Control with 1 transistor , I used it to drive an LED (see the comments to that blog). The current switched pretty quickly and I wondered how it would compare to driving a simple resistor: just how fast can an LED be? Simple way to find out was to try it, so here's a shoot-out between a blue LED and ...
Last week I did a blog where I looked at the response of an LED to light: Experimenting With Using an LED as a Light Sensor . I thought it might be interesting to extend that a little bit further.   As before, the input is a reverse-biased LED acting as a photodetector. Again, I'm going to use an op amp as a transresistance amplifier (this time a Microchip device that can operate on 5V) but, for a bit of added interest, instead of generating an output voltage that's linear with diode cur ...
Does an LED work as a light sensor? Short answer is yes. That's fairly well known, but I've never tried it myself, so here goes.   I'm going to use a couple of old high-brightness red LEDs. I don't know much about them other than that they are definitely high in brightness, have a narrow viewing angle, and the package is 'crystal clear'.   My light source is an Arduino flashing one of the LEDs five hundred times a second [if jancumps can do a 'blinky', so can I!]. I've got a 330R res ...
Introduction   In a recent thread here, I mentioned to dubbie that it might be possible to use the balanced modulator in an RF mixer chip to create a Dalek sound effect. Later on, I discovered that I had a couple of them [in the old DIL package, too], so I though I'd do a quick bit of hardware hacking and see how they manage at audio frequencies. The mixer is based on a Gilbert cell, which will, of itself, work right down to dc, but there is internal biasing of the transistors, which t ...
jc2048

Bauble

Posted by jc2048 Dec 27, 2019
Recently, element14 was kind enough to send me a 'swag pack' which included a solderless breadboard. I wondered what to do with it as a quick blog and then remembered a small and very simple experiment I had thought of some time back and never tried.   My starting point was this episode of The Learning Circuit 32:  Making a FET Phase Light where Karen gave us a circuit to sequence three LEDs. Perhaps I could extend it and make it a ring of nine sections. Would that work? We'll see ...
jc2048

Swag Pack November 2019

Posted by jc2048 Nov 26, 2019
Received this 'swag pack' last week.       Not sure why I got it, but thanks anyway. I like the Faraday and Lovelace stickers, they're cool. I'll see if I can do something with the Uno. ...
Introduction   NIC stands for Negative Impedance Converter. It's one particular circuit configuration that can exhibit the phenomena of negative resistance. I'm going to look at that first and then, once we've done that, I'm going to use a pair of them to power a rather curious oscillator circuit due to Chua (the fun bit).   An Op Amp Negative Impedance Converter   As I'm sure you all know, a simple passive resistor has a property called resistance. The resistance is the con ...
jc2048

Chaos

Posted by jc2048 Apr 30, 2019
I've just been playing with Chua's circuit, using a couple of op amps for the negative resistance element. It makes for some pretty XY plots on the oscilloscope. Thought you might like to see them.       It's very finicky getting the values right and you can see from the bottom trace that it's not very stable, but it's good fun to play with.   Here's a link to the follow-up blog where I go into more details about the circuit I was using: Op Amps: NIC (Negative Impedanc ...