Hi! I working on a robotics project... Check it out! Do drop a like too :P

https://hackaday.io/project/165046-autonomous-navigation

Thank you, Revision, so the challenge for the spectrometer is to find a white LED with a flat respsonse at least over the visible range of the spectrum.
I understood, that all the these gadgets are expected to work 'stand alone'.
Nevertheless it would be great, if could allow for further experiments by combining them.
For example the famous NE555 could act as a sensitive Lux-meter with the very same LED
(voltage/resistance to frequency converter). The said diffraction grating usually suffer from a very small spread angle. Probably a cheap glas(tube) filled with water and a homemade gap made from black  carton will do better and is at least as educational, of course that would limit you to a single source of light (other than in one of your other projects).
Anyhow I like the idea, though the desired 1$ Limit will require high quantities (>1000).
I'm sure the community will soon contribute ideas for further items. Good Luck!

I supposed the light from an LED to be monochrome or composed from a few colors to make our eyes see e.g white - how can that work?
Peter/DL3PB

Hi Peter. Forr the spectrometer kit, i was thinking a right white LED so as to have a reliable(ish) light source for the basic experiments. I did think of different colour LEDs for further experiments, but that may make the kit too expensive. My understanding is that LEDs can emit light from a single nm wavelenght to and entire range, so i will look for the main one to cover 400-700 nm visible range, without to many peaks.