From: Bdale Garbee <bdale@gag.com>
Date: Wed, 30 May 2018 14:23:54 +0000 (-0600)
Subject: document what's required to make the 12V switcher on v2.0 work
X-Git-Tag: fab-v2.1~20
X-Git-Url: https://git.gag.com/?p=hw%2Ftelelco;a=commitdiff_plain;h=4d9c837e4c96d64724f1a2666ab1b620d0e39a0e

document what's required to make the 12V switcher on v2.0 work
---

diff --git a/Notebook b/Notebook
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+2018.05.30
+
+To make v2.0 useful:
+
+Replace the 27k in the lower leg of the AP3012 comparator circuit with a 56k
+to drop the voltage from ~27V to just under 12V.
+
+In the AP3012 circuit, rotate the inductor and 4.7uF caps 90 degrees, and lift
+pin 5 of the IC, to detach all of them from the 3.3V rail.  Use a wire to 
+connect all of them to pin 4, the gpio driving the circuit.
+
+The net effect is that we're making 12V from the gpio, which means all the LED
+current and switcher inefficiency is coming as current through that gpio.  The
+measured LED current is around 7mA, so this is "safe" for the SOC, but really
+not a great plan... 
+
+Need to redesign this in the future to use a transistor/FET switch.