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diff --git a/src/attiny/ao_adc_attiny.c b/src/attiny/ao_adc_attiny.c
new file mode 100644
index 00000000..3a835d13
--- /dev/null
+++ b/src/attiny/ao_adc_attiny.c
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+/*
+ * Copyright © 2017 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <ao.h>
+
+/*
+ * ATtiny ADC interface
+ */
+
+uint16_t
+ao_adc_read(uint8_t mux)
+{
+	uint8_t	low, high;
+
+	/* Set the mux */
+	ADMUX = mux;
+
+	/* Start conversion */
+	ADCSRA = ((1 << ADEN) |
+		  (1 << ADSC) |
+		  (0 << ADATE) |
+		  (0 << ADIF) |
+		  (0 << ADIE) |
+		  (0 << ADPS2) |
+		  (0 << ADPS1) |
+		  (0 << ADPS0));
+
+	/* Await conversion complete */
+	while ((ADCSRA & (1 << ADSC)) != 0)
+		;
+
+	/* Read low first */
+	low = ADCL;
+	high = ADCH;
+
+	return (((uint16_t) high) << 8) | low;
+}