Work out the series resistor an LED needs, rounded up to the nearest E12 value, with a safe power rating.
LED Resistor Calculator runs in the page as you use it. There is no input to submit and no result to fetch, because the whole thing happens on this side of the wire.
Everything runs client side, which is the only arrangement where a privacy claim is checkable. Open the network tab and watch it stay empty.
You will find it under Engineering, alongside 8 other tools for the same sort of job.
Runs in this tab, so nothing you type is uploaded.
supplyVoltageVolts: 9 ledForwardVoltageVolts: 2 ledForwardCurrentMilliamps: 20
Resistance ohms: 350 Nearest e12 ohms: 390 Actual current milliamps: 17.9487 Power dissipated watts: 0.1256 Recommended power rating watts: 0.5
Yes. It is JavaScript running in this tab, so once the page has loaded it needs nothing further from the network. Put the machine in flight mode and it carries on. Nothing you do here is sent anywhere, because there is nowhere for it to go.
No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.
Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.
Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.
Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.