Rant: The EV number plate design

Posted under Educational, Product Design on October 30th, 2022 by

I have been driving around and I keep finding this very irksome. The electric vehicle number plate colour choice in India is plain ridiculous in my opinion. For those in my network who don’t know what I am talking about, the number plates for EVs in the Indian market is now designed with a full-length light green background with a pure white text colour for the actual numbers. The white text colour is for private vehicles and it gets replaced by yellow text for commercial vehicles. For normal petrol/diesel private vehicles, it’s pure black text on a white background.

What’s my problem with EV number plates? There is very little contrast in the colour of white and a light green background. It’s pretty hard to distinguish or read out colours because of the lack of contrast esp. at night. Now add to the case that, if your vehicle headlights shine a bright light directly on an EV’s back number plate, the light green kinda shines bright and makes the contrast to read out the white text even harder. This becomes practically worse for a commercial vehicle with yellow text and light green background with minimal contrast. To add to this, contrast is affected more by the fact of littering of the word IND across the text in pure black which makes it the absolute worst colour choice since it reduces the reflection of the white text. All of this becomes problematic when you try to read a number plate in an emergency scenario.

I personally cannot think of any reason why govt would roll out this colour scheme without looking into these aspects. A simple way they can fix this is by increasing the darkness of the green so that there is enough contrast. There are 10s of shades in each colour, pick a pair which can give maximum contrast. There are enough colour contrast checkers available online for free to test this.

Am I the only person to be disturbed by this? Am I missing something obvious which govt thought of? I really would love your opinions on this one.

PS: It’s a deviation from my usual posts. But I had to put this out there. Sorry for the not-so-great photo, Took it while driving.

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Simplest Constant Current Driver IC

Posted under Educational, Product Design, Technology on October 9th, 2022 by

If you are ever trying to drive LEDs in your circuit, you always do it with a constant current driver. You don’t use a constant voltage drive with maybe a resistor to regulate current because not all LEDs are made equal, even in the same batch. The forward voltages of LEDs do change, when that changes, the effective brightness will also change, when you drive it in a constant voltage mode. So whenever you are driving multiple LEDs or want to maintain a constant brightness always use constant current drivers.

Recently ran across AL5809 which is an ultra simple 2-pin constant current driver IC which will fit the package dimensions of small SMD resistors. These come in various options of current regulation from 15mA-150mA. The nice part about this is that you can string multiple of these in parallel and can get even more current in a single channel. So you can use them in a wide variety of LED use cases. Internally it contains a fixed resistor with a current mirror which gets changed in each version of the IC. You need to provide a voltage of at least 2.5V across these terminals more than the series voltage drops of your LEDs. So think of it as adding one LED in series to your LED string to regulate the current.

It does support PWM dimming also with an external MOSFET to dim the brightness from 5% to 95% at a frequency of 100Hz. This is kinda low because if used in photos/video applications, you will see flickering of the LEDs. I do think it can be driven at higher rates but the regulation might not be linear anymore. One major thing to consider for these ICs, is their power dissipation, Whatever the extra voltage is in the rail after adding up the forward voltages of LEDs, should be dissipated in these ICs. So if you have a 24V line and only 2 LEDs with 3V drop each would mean 18V is dropped across this IC. If it’s rated for 150mA, Power dissipation will be 18V*0.15mA = 2.7W which exceeds the package’s thermal capabilities unless you cool it externally.

Anyways nifty little chip, worthwhile considering because of its simplicity, accuracy, price and size in your next LED project.

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