Soldering is one of those jobs that are conceptually simple enough, but there’s quite a bit of devil in the detail and having precisely the right tool for the job in hand is essential for speed and quality of results. The higher-quality soldering stations have many options for the hot end, but switching from a simple pencil to hot tweezers often means unplugging one and reattaching the other, and hoping the station recognises the change and does the right thing. [Lajt] had three soldering options and a single output station. Their solution was a custom-built three-way frontend box that provides a push-button selection of the tool to be connected to the station sitting atop.
[Lajt] shows in the blog post how each of their target hot ends is wired and the connectivity the control station expects to determine what is plugged in. Failing to recognise a connected 50 W heating element as if the smaller 25 W unit was still connected would suck, with a huge amount of lag as the temperature of the hot end would fail to keep up with the thermal load during use. When connections are made, it is important to ensure the unit has sufficient time to detect the change in output and configure itself appropriately. An Arduino Pro mini handles the selection between outputs by driving a selection of relays with appropriate timing. An interesting detail here is what [Lajt] calls a ‘sacrificial relay’ in the common ground path, which has a greater contact rating than the others and acts as a secondary switch to save wear on the other relay contacts that would otherwise be hot-switched. All in all, a nicely executed project, which should offer years of service.
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