Hello everyone,
I'm building a prototype research system for studying the pupil's response to light. I have an integrating sphere, and now all I need is a light source to shine into it that ideally meets the following requirements:
- Is relatively high power
- Has red, green, blue and white channels
- Can be controlled with good temporal accuracy (e.g. a 1 second pulse of light)
- Can be modulated in brightness (e.g. a sinusoidal profile from mimum to maximum brightness)
- Can be controlled in real time from a Python script
I'm relatively new to Arduino and electronics, but have figured out how to use pyFirmata to PWM a simple LED mounted on a bread board. We will use a 40 W RGBW LED (https://www.mouser.co.uk/ProductDetail/LED-Engin/LZC-B3MD07?qs=ykpMnEfb%252BJzKA%2Fze773Sgg%3D%3D), so there will be need for a power supply and a transistor / relay component to the circuit (though I don't have much experience with this).
I'd really appreciate any comments / suggestions regarding the components, circuitry, and Python implementation.
Thanks and regards,
Joel
Edit: Here is a picture of the integrating sphere with a high-end light engine installed. The idea is to replace that with something more affordable!
Ok you will need a hefty constant current circuit to drive and as you need to dim it with PWM you will need a dimmable constant current circuit.
Also it will get very hot in an enclosed space, so you might need some ventilation at the back and a large heat sink.
A bit of a tough assignment for a beginner.
Thanks for replying Grumpy_Mike. Yes, it is a tough one for a beginner, but thankfully I will have access to local expertise when work resumes back in the office. My job is to get things moving, so I'm currently assembling a parts list and thinking about the circuit / Python implementation. The parts I have so far are:
LED - https://www.mouser.co.uk/datasheet/2/228/5412941_2520LED_2520Engin_Datasheet_LuxiGen_LZC-03-1531996.pdf
Diffuser - https://www.mouser.co.uk/datasheet/2/228/LED_2520Engin_Datasheet_Optics_LLNF-3T08-H_LLFL-5T-1531893.pdf
Heat sink - https://www.mouser.co.uk/datasheet/2/433/PIN_LED_Heat_Sink_Wakefield_Vette_Data_Sheet-1624808.pdf
Currently researching power supply, thanks for the tip.
The LED will be mounted at the top of the sphere pointing into an entry port (concealed by the light engine in the picture), and typical usage will be in 1-5 second pulses of light, or 30 second sinusoidal modulations. So with no constant usage, am I right to think that thermal management will not be such a big problem?
I'll update the thread with progress once the parts are sourced and the prototype is developed.
If the python is running on the Raspberry Pi then you can generate PWM with that. No need for an Arduino.
Good to know, but I'd need to be able to control the Pi from a script running on a laptop, as the LED needs to be integrated with other hardware that is not compatible with Raspberry Pi.
with other hardware that is not compatible with Raspberry Pi.
I find that very hard to believe, especially as you imply that it is compatible with the Arduino. There are very few things in this world that you can’t interface to given the right circuit. I have been designing circuits like this for most of my life. In the 60s in my first job when I left school I was on a project to interface an IBM main frame computer with a Swiss weaving machine that used compressed air to blow the weft from one side to the other.
I need to integrate the light with a high-end eye tracking device that streams 3 cameras at 120 Hz, and which runs on software that is not available for the Pi. So that's why I'd like to be able to control everything from a Python script running on a windows / mac laptop. The arduino / pi is simply for hosting the circuit and driving the LED. Ideally I will connect via USB and send commands from the laptop. I know that's possible with arduino and pyFirmata, but not sure about Pi.
That's a cool story, you must have so much knowledge in this business!
Grumpy_Mike:
Ok you will need a hefty constant current circuit to drive and as you need to dim it with PWM you will need a dimmable constant current circuit.
Would this be a suitable power source for driving the LED?
https://www.mouser.co.uk/ProductDetail/ERP/ESM050W-1200-42?qs=ViQZ5ZvlJQsPaoDe9h4j1A%3D%3D
Would this be a suitable power source for driving the LED?
A bit too much current. Your LED has a maximum current of 1000mA and working current of 700mA, that current drive gives 1.2A.
Look at page 15 of the data sheet, you will need four constant current drives, one for each of the four colours. Also note it recommends a soldering iron of greater than 60W.
and which runs on software that is not available for the Pi.
In my book it is just the software and not the hardware that is incompatible with the Pi.
This looks like it would do the job, then, as it has 4x1000 MA outputs and supports PWM dimming.
https://www.mouser.co.uk/ProductDetail/Cincon/MLD4-C100?qs=1KA9tXninq4f82E41PeS9A%3D%3D
In my book it is just the software and not the hardware that is incompatible with the Pi.
OK, I agree with this. But affordability and accessibility are key motivations for this project. I'd like other potential users with limited resources to be able to replicate this with minimal expertise, and to integrate it with tools that they are already familiar with.
Looks OK, but the data sheet doesn’t specifically say it is PWM dimming, user capable with a module.
On page 3, under MLD Series it specifies 'Constant Current Dimming Control (PWM mode)'
And on page 9, 'Input Voltage Range -- TTL logic compatibility -- 5 -- Vdc
