add LARS page

input/projects/lars.md

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+title: LARS - Looping Automated Rhythm Station
+description: Loopstation drumkit with hand-made solenoids and RP2040
+parent: projects
+git: https://git.xythobuz.de/thomas/drumkit
+date: 2024-03-25
+comments: true
+---
+
+For the recent birthday party of one of our [DrinkRobotics](drinkrobotics.html) and musician friends, [Kauzerei](https://github.com/kauzerei) had the great idea to build a DIY drummachine as a present, to allow them to play the bass without having to gather a jam session group.
+He recruited me for some electronics design brainstorming and to write the firmware.
+
+<!--%
+lightgallery([
+    [ "img/lars_3.jpg", "LARS drum and controller. © 2024 Kauzerei." ],
+    [ "img/lars_7.jpg", "LARS logo" ],
+    [ "img/lars_10.jpg", "LARS actually running" ],
+])
+%-->
+
+It is mainly made out of repurposed old parts from the recycling bin.
+The drum body consists of a tambourine with a 3D printed frame attached, with three hand-wound solenoids mounted on there.
+The positioning and different hammers create some (slightly) differing sounds.
+
+<!--%
+lightgallery([
+    [ "img/lars_8.jpg", "Solenoids mounted to frame" ],
+    [ "img/lars_4.jpg", "LARS on table. © 2024 Kauzerei." ],
+])
+%-->
+
+The electronics are made with a Raspberry Pi Pico (or Pico W in this case, although WiFi or BT are not used yet).
+This keeps the future option of a USB Midi input open.
+The user interface consists of four buttons, each with an LED above, and a clickable rotary encoder, as well as a power switch and an 128x64 SSD1306 OLED display.
+To drive the solenoids, three step-up converters create ~16V from the single Li-Ion 18650 cell.
+Their output is then switched to the solenoids using MOSFETs.
+A small TP4056 module handles recharging the battery.
+
+<!--%
+lightgallery([
+    [ "img/lars_14.png", "Schematic" ],
+    [ "img/lars_11.jpg", "Step up converters" ],
+    [ "img/lars_12.jpg", "LED and button for panel mounting" ],
+])
+%-->
+
+All of this is mounted on a custom hand-etched PCB.
+
+<!--%
+lightgallery([
+    [ "img/lars_15.png", "PCB layout" ],
+    [ "img/lars_13.jpg", "PCB with photoresist, before etching" ],
+    [ "img/lars_9.jpg", "Side view of case/pcb sandwich" ],
+])
+%-->
+
+We only came three hours late to the birthday party due to finishing the LARS hardware, and I spent some more time at the party putting some final work into the firmware.
+It actually was functionally usable on the party evening, even before everyone was too drunk to care 🥴
+
+<!--%
+lightgallery([
+    [ "img/lars_16.png", "PCB 3D render back" ],
+    [ "img/lars_17.png", "PCB 3D render front" ],
+])
+%-->
+
+Unfortunately there was no time yet to take good pictures or a video of LARS in action.
+
+As usual all 3D print files, PCB layout design and firmware source code is [available in the repo](https://git.xythobuz.de/thomas/drumkit).
+You can also order the PCB pre-fabricated from an online supplier, the repo includes a script to generate the gerber files.
+
+The software is not quite finished yet, but without access to the hardware I'm not really able to work on it further.
+
+For now.
+
+## More Pictures
+<a class="anchor" name="more_pictures"></a>
+
+<div class="collapse">Some more photographs I didn't use above.</div>
+<div class="collapsecontent">
+<!--%
+lightgallery([
+    [ "img/lars_1.jpg", "LARS front panel. © 2024 Kauzerei." ],
+    [ "img/lars_2.jpg", "LARS on table. © 2024 Kauzerei." ],
+    [ "img/lars_5.jpg", "LARS on table. © 2024 Kauzerei." ],
+    [ "img/lars_6.jpg", "LARS on table. © 2024 Kauzerei." ],
+])
+%-->
+</div>