From d4d9fd71dd675c77752d06b52b5472422976d735 Mon Sep 17 00:00:00 2001
From: Ben Harris <bjh21@bjh21.me.uk>
Date: Wed, 27 Jan 2021 09:45:46 +0000
Subject: [PATCH] Brief notes on the requirements for Q1

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 index.xhtml | 4 ++++
 1 file changed, 4 insertions(+)

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@@ -51,6 +51,10 @@
       achieve 1.24 V across R1.  D1 suppresses any voltage spike
       caused by the inductance of the clock coil.  The whole thing
       turns off when the GPIO line goes low.</p>
+    <p>The specifications of Q1 are critical.
+      It needs a high enough <var>h<sub>FE</sub></var> and a low enough
+      <var>V<sub>BE</sub></var> that it can sink 250 mA when driven
+      by the relatively weak output of a Raspberry Pi GPIO.</p>
     <h2>Use</h2>
     <p>Plug the board into a Raspberry Pi with the square solder pad
       connected to pin 1 of the GPIO connector.  Connect the clock
-- 
2.30.2