About

I am a ‘retired’ university professor. A biologist by training, my professional expertise lies in the area of electrophysiology and biophysics. My time is now spent travelling, taking photos, driving absurdly fast cars and building improbable bits of kit. I live part of the time in the Tarn, France, near a small village called Penne. I have a website at www.petermobbs.com where you can see some of the photos I have taken of the butterflies, other insects and the landscape around Penne.

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2 Responses to About

  1. Steve Chambers says:

    I have a question about your circuit . I am curious of the purpose of the 1 microfarad capacitor in parallel with the 1000 microfarad bank. I have some 5 watt that I have found to be a good balance of brightness to heat that I think I will try this on. Would you be willing to share your code ? I have followed your adventures on the camera axe forums, you have some brilliant ideas and great photographs. Steve Chambers

    • petermobbs says:

      Hi Steve, Thank you for your kind words.

      The small capacitor is mainly there because the circuit was largely copied from the paper by Willert et al. and they had one in that location! However, I think it comes under the heading of a decoupling capacitor sending any high frequency noise on the power supply line to earth. As to the code to drive the flash, yes, I will share it but at present it exists only as a simple loop that sets a digital pin high and then, after a delay, sets it low again. That works fine for ON periods of greater than ~5us. For shorter times, one needs to use the ‘PORT’ command and insert ‘no operations’ (nop) commands between writing to the port to set the pin ‘high’ and then writing to it again to set it low. While using those commands, I can get 1/2,000,000th of a second flashes, they are really, really, feeble. I may be able to speed the rise-time up a bit by improving the layout of the circuit – this will increase the brightness a bit. However, I doubt that flashes of less than a few microseconds are ever going to be very useful using the low power chips that I am.

      My plan now is to write some code to control a pair of LED flashes. The code will allow the flashes to operate in stroboscopic, and triggered single flash, mode. A couple of switches will allow the LED to be operated continuously – they are really bright and will make great modelling lights for my macro setup.

      Bottom line…..some more sophisticated code (or at least something a bit more useful) will appear soon.

      Let me know how you get on with the 5W chips. All the best, P.

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