Comments on: Drive 4 digit 7-segment LED displays direct from a micro:bit http://www.suppertime.co.uk/blogmywiki/2021/04/microbit-7-segment-led/ reading, writing, coding, making Tue, 24 Oct 2023 13:43:21 +0000 hourly 1 http://wordpress.org/?v=3.1 By: Johan Halmén http://www.suppertime.co.uk/blogmywiki/2021/04/microbit-7-segment-led/#comment-103036 Johan Halmén Fri, 25 Mar 2022 05:25:59 +0000 http://www.suppertime.co.uk/blogmywiki/?p=3846#comment-103036 A 300 ohm resistor is way too big for the led, but probably very good for the Microbit. On this page: <a href="https://tech.microbit.org/hardware/powersupply/" rel="nofollow">https://tech.microbit.org/hardware/powersupply/</a> ...it says: <cite>The on-board current budget will vary depending on the use of the display, the Bluetooth, microphone, speaker and other peripherals. You should allow a worst case budget of 30mA for when all on-board peripherals are in use, leaving V1 90mA / V2 270mA for circuits plugged into the edge connector.</cite> The optimal current for one led segment is 20 mA. That makes 140 mA for one digit showing all segments. Add another 20 mA for the decimal point. The V2 Microbit can handle that, but not the V1 Microbit. I'm about to build something out of my Microbit and this kind of 4*7 segment display, but I only have a V1 Microbit. So I'm afraid I have to use a set of transistors to make that happen. A 300 ohm resistor is way too big for the led, but probably very good for the Microbit. On this page:
https://tech.microbit.org/hardware/powersupply/
…it says:
The on-board current budget will vary depending on the use of the display, the Bluetooth, microphone, speaker and other peripherals. You should allow a worst case budget of 30mA for when all on-board peripherals are in use, leaving V1 90mA / V2 270mA for circuits plugged into the edge connector.

The optimal current for one led segment is 20 mA. That makes 140 mA for one digit showing all segments. Add another 20 mA for the decimal point. The V2 Microbit can handle that, but not the V1 Microbit. I’m about to build something out of my Microbit and this kind of 4*7 segment display, but I only have a V1 Microbit. So I’m afraid I have to use a set of transistors to make that happen.

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