Thanks James. I haven't seen the last item "Raspberry Pi 4 Model B" data sheet before.

Thanks as well Burngate - all helps the understanding

But inputs are effectively open circuits

The penny has dropped! Thanks guys for your patience and fast responses. I shall proceed as built

Hi Gordon The actual current in or out of the pin will be determined by whatever internal pull-up or pull-down, if any, has been enabled. I'm having trouble getting my head round this. If there are no internal pull-up or pull-down enabled (which is the state on boot) then there is no internal resist...

How did you measure the current, without connecting to the Pi? The Pi input will be high impedance, so very little current will flow (different if you activate either pull-up or pull-down on the input). The 1k resistor will protect things when the GPIO is accidentally set as an output. In all cases...

This http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/raspberry-pi/gpio-pin-electrical-specifications says 16mA. Thanks Gordon. Actually the article also quotes "never source or sink more than 0.5 mA into an input pin." (Section RPi GPIO input voltage and output current li...

Hi. After 2 years I'm getting back into Pi hardware and having to relearn again! Some help appreciated so I don't fry my new Rasp Pi 4 ;) I've designed and built (but not connected to the GPIO pins yet) interface circuitry using the typical 10K & 1K pull up and down resistor circuits, for example: G...

I managed to get this working for my situation by successfully tethering the Pi to the phone and removing the Draytek gateway from the Pi routing table. So for the benefit of any people directed from a google search here's what I did. First thing to say is I learnt that Pi networking changed substan...

Hi I have a presentation next Tues to U3A on the internet of things and wish to demonstrate IoT gadgets that I have using Node-Red on a Raspberry Pi 3 with Jessie (up to date). One of the demos accesses devices on the LAN and services in the cloud. But the venue has no internet so I thought I would ...

I spent a day working on this to connect a BT speaker (BETRON KB-S08 or KBS08) and eventually got it working without using the GUI. [In this post I've left in many comments after the command lines, so it's best to copy all of this to a text file and then copy and post the commands] 1. To start with ...