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Messages - nickjohnson

1
Project development, ideas, and suggestions / My newest project: Tsunami signal generator and analyzer
I've been working for a while on my newest project, which I'm calling the Tsunami, and it's finally ready to go! It's an arduino-based signal generator, frequency counter, and analog experimentation board.



After the success of the Re:load Pro (incubated in part here on the DP forums!), I've decided to kickstart it again - it's up here.

As always, feedback greatly appreciated. :)
2
Project development, ideas, and suggestions / Re: uCAN: A protocol stack for microcontroller networking
[quote author="Dro"]Hey Guys,

Not sure if there has been any progress regarding uCAN but I am currently looking for a Higher level application for a home automation project that I have started. I considered using both CANopen and VCSP and looks like I felt the same way you guys feel.

I did find the following CANopen library that was originally created for PIC and accordingly to the author it should be fairly easy to port to other uCs. I am not sure if anybody wants to take a stab at it.

http://sourceforge.net/projects/canopennode/

Let me know if this project is still going so I can see if I can use it for CAN home automation. My board is based on ATMega328p running Arduino bootloader + MCP 25625.

Thanks,

Dro[/quote]

It's been more or less on hold for me for a while since I've had other things to work on like my kickstarter, but I certainly intend to pick it up again soon.
3
Project development, ideas, and suggestions / Re: Detecting high speed light flashes
[quote author="Bertho"][quote author="nickjohnson"]Why AC-coupled? The schematic I'm using does reverse bias it, but I'm prepared to put up with the dark current, since I'm not looking to measure small signals.[/quote]
The signal you measure may be large, but the response-time of the diode is in large part dependent on the capacitance. In a 3.3V or 5V system you generally have not enough margin to drive the diode to its lowest possible capacitance. Most diodes can be reverse-biased at 15V or more (very high-speed diodes at 100..200V).

The PN barrier will increase size with higher reverse-voltage and thereby reducing the effective capacitance of the barrier. Electron jumps will then result in a larger voltage step because the charge change is not absorbed in the a high capacitance (Q=C*U --> U=Q/C). At high reverse-bias you need fewer electrons to jump to see the same delta-U on the output, effectively making your system faster.

However, your electronics beyond the photodiode will most likely run on a lower voltage. Therefore you need to do DC isolation to protect your logic. Therefore you need AC-coupling. Your trigger system will probably work on edge triggering just as well as level-triggering. Considering the speed of the pulse, you probably already use edge-triggering.[/quote]

I'm not sure I follow - however high the bias voltage, the voltage on the amp side will be low. The diode is reverse-biased, after all.

At any rate, with -5v bias voltage, the Analog tool claims I ought to have 63.5dB SNR, assuming a maximum of 4w/m illumination (these are _very_ bright flashes of light).
4
Project development, ideas, and suggestions / Re: Detecting high speed light flashes
[quote author="Bertho"][quote author="nickjohnson"]I'm aware how many orders of magnitude it is. :) Alternately, it's a one-SI-modifier mishap.[/quote]
I'd argue against a SI modifier mishap because the SI-unit for seconds is lower-case 's'. Just to be pedantic ;-)
(couldn't resist)

Quote
As long as the delay is consistent, this won't be an issue. The flash of light is what triggers capture, so absolute timing is not essential.
Consistency should be no problem. The trick when using "cheap" photodiodes is to do AC coupling and a suitable amplifier stage. Then you can drive the photodiode in reverse with a high voltage to lower the effective capacitance and at the same time increase the yield (in case of a pin- or avalanche-diode).[/quote]

Why AC-coupled? The schematic I'm using does reverse bias it, but I'm prepared to put up with the dark current, since I'm not looking to measure small signals.
5
Project development, ideas, and suggestions / Re: Detecting high speed light flashes
[quote author="Bertho"]Ok, that is a three orders of magnitude mishap. However, it completely changes the game and now /most/ photodiodes with reasonably low capacitance will be sufficient. A 100..200MHz GBW opamp should also be enough to get a sane signal too.[/quote]

I'm aware how many orders of magnitude it is. :) Alternately, it's a one-SI-modifier mishap.

Quote
You _do_ have to take into account that the group-delay of the system will be dependent on the quality of components. You may see a signal at the output that has 0.1us...10us delay, depending sensor and opamp.

As long as the delay is consistent, this won't be an issue. The flash of light is what triggers capture, so absolute timing is not essential.

I'd still be keen to find a better suited photodiode in the visible range; that one was the best available in the tool, or on Farnell, in that range, since it's got the lowest capacitance by a substantial factor.
9
Project development, ideas, and suggestions / Detecting high speed light flashes
I need to detect - and measure on a 'scope - short pulses of light on the order of 1 microsecond. The pulses are very bright, so sensitivity isn't a big issue, just bandwidth and rise time. Simplicity is an asset, since this is a one off requirement.

I figure I probably need a photodiode and a high speed transimpedance amp, but most amps cap out below the 1MHz range, and many that don't are quite complex to interface with and compensate. Any suggestions?

Edited: Microsecond, not nanosecond.
11
Project development, ideas, and suggestions / The Re:load Pro, a DP alumni, on Kickstarter
Some of you may remember the original Re:load, which I designed with the help of others here on the DP forum. I designed the original Re:load to fill a need of my own, and out of frustration at the lack of any good alternatives available to electronics hackers. It turns out that I'm not the only person who found a lightweight and robust active load a useful tool, and the Re:load's turned into a popular and well-regarded product.

Today I'm finally launching the Re:load Pro on kickstarter. The Re:load Pro takes all the advantages of the original Re:load, and improves upon them with a robust benchtop case, a good quality display and UI, an isolated USB interface, and an integrated processor - the PSoC 4 from Cypress - that together make it an extremely sophisticated and versatile piece of equipment.

I wouldn't have got this far this fast without the help and support of everyone here on DP. Thanks! I'd love to hear what you think of the Pro, and if you're going to back it.
12
Hardware biz / Re: Tindie commission increase
[quote author="t0mpr1c3"]I think the Tindie "all time favourites" list is really more like "flavour of the month" because the blinky valentine's heart kit I sold 10 of last week is now showing up higher than Digispark, which I'm guessing has total Tindie sales in the hundreds if not thousands.[/quote]

Yes, it uses a 'frecency' algorithm - that is, a combination of the number of sales and how recent they are.
14
Project logs / Re: holiday break project
[quote author="Sjaak"][quote author="nickjohnson"]
Sorry, just now saw this. It's a 160x64 COG display from buy-display: buydisplay.com/default/cog-160x64-lcd-module.html[/quote]

How are the shipping costs? the prices of the modules are dirt cheap.[/quote]

For a small order of 4 displays, it came to more than the items. For larger orders I think it'd be pretty tolerable.