Five volts is allowed here
The 150 Ω resistor is fixed and the LED drops about 1.2 V, so VCC alone sets the current: about 13 mA from 3.3 V and 24 mA from 5 V, for about a third more reach. Both are far inside the LED's 100 mA. The part that runs out first is the resistor, near 5.7 V, so 5 V is the top.
One wire decides the current
On most TinkerBlock blocks VCC must be your board's logic voltage. Here it is a choice, because VCC never reaches SIGNAL. And it is the one choice that changes how much infrared comes out, because nothing else on the board can.
Move the slider. The current is what is left of VCC after the LED's 1.2 V and the transistor's small drop, divided by 150 Ω: about 13 mA from 3.3 V and 24 mA from 5 V. These are worked out from the data sheet's typical figures, not measured, and a given LED may be a little off either way.
What 5 V buys
The light an LED gives rises roughly with its current, and the light that reaches a receiver falls with the square of the distance. So the reach goes with the square root of the current: 24 mA against 13 mA is about a third more distance. For moving one wire, that is the biggest thing you can do for range, and your pin does not change.
Where it stops
The LED is rated for 100 mA continuous, so 24 mA uses about a quarter of it. The 150 Ω resistor is closer to its limit. It is an 0805 part rated for 1/8 W, and with the LED held on from 5 V it dissipates about 89 mW, some 70 % of that. It would reach its rating near 5.7 V, long before the LED reached 100 mA, which would take about 16 V.
TinkerBlock blocks are built for 3.3 V or 5 V, and 5 V is the most any of your boards offers, so there is no higher rail to reach for. Sending a remote-control code is gentler still: the carrier keeps the LED on for under a third of each cycle.
When it does not work
VBUS, which carries the USB supply and so is 5 V only while the Pico is plugged into USB. On a battery, use 3V3; the block works, over a shorter distance. VSYS is whatever feeds the Pico and may be lower.
It can be. With the LED held on from 5 V it turns about 89 mW into heat, about 70 % of its 1/8 W rating: warm, and within it. Sending a remote-control code keeps the LED on for less than a third of the time, so it runs much cooler.
Not safely by guesswork. A smaller resistor at 5 V pushes more current through itself and the LED, and the 0805 resistor is already at 70 % of its rating when the LED is held on. Aim, distance and shade on the receiver buy more than a hotter LED.
Where the light goes, how wide, and at what wavelength.
A narrow beam you cannot see →Edit this page — content/books/ir-transmitter/five-volts-is-allowed-here.mdx
Questions about this product
See what other owners have asked, and read their solutions.
Infrared Transmitter
Loading discussions…
Discuss this article
Ask about this page. The answer stays here, on the page it belongs to, for whoever hits the same wall next.