From cdf2a5026e45ac2b65001ed41cc67d86590a681a Mon Sep 17 00:00:00 2001
From: Tomasz Kramkowski <tomasz@kramkow.ski>
Date: Thu, 16 Oct 2025 19:33:17 +0100
Subject: Driver example

---
 src/dual_hx711.rs | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 src/dual_hx711.rs

(limited to 'src/dual_hx711.rs')

diff --git a/src/dual_hx711.rs b/src/dual_hx711.rs
new file mode 100644
index 0000000..13ec247
--- /dev/null
+++ b/src/dual_hx711.rs
@@ -0,0 +1,75 @@
+// SPDX-FileCopyrightText: 2025 Tomasz Kramkowski <tomasz@kramkow.ski>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//! Driver for reading from two HX711 ADCs with a shared clock.
+//!
+//! (Datasheet)[https://cdn.sparkfun.com/assets/b/f/5/a/e/hx711F_EN.pdf]
+//!
+//! Existing implementations could not handle a combined setup.
+
+use embassy_stm32::timer::GeneralInstance4Channel;
+use embedded_hal::digital::InputPin;
+use embedded_hal_async::digital::Wait;
+
+use crate::pulse::Pulse;
+
+/// Dual HX711 driver
+pub struct DualHx711<'a, T: GeneralInstance4Channel, A: InputPin + Wait, B: InputPin + Wait> {
+    clock: Pulse<'a, T>,
+    a: A,
+    b: B,
+}
+
+/// Sign extend a two's complement number stored in the low 24 bits of a u32 to
+/// an i32
+fn convert_c24_to_i32(n: u32) -> i32 {
+    ((n << 8) as i32) >> 8
+}
+
+impl<
+        'a,
+        T: GeneralInstance4Channel,
+        E,
+        A: InputPin<Error = E> + Wait,
+        B: InputPin<Error = E> + Wait,
+    > DualHx711<'a, T, A, B>
+{
+    /// Create a new driver from clock and data pins
+    ///
+    /// Clock pin must be a `Pulse` configured to produce an appropriately timed
+    /// clock signal. Refer to the HX711 datasheet for more details.
+    ///
+    /// Currently only implements CH.A, Gain:128 mode
+    pub fn new(clock: Pulse<'a, T>, a: A, b: B) -> Self {
+        Self { clock, a, b }
+    }
+
+    /// Read the next available conversion from both HX711s
+    pub async fn read(&mut self) -> Result<(i32, i32), E> {
+        self.a.wait_for_low().await?;
+        self.b.wait_for_low().await?;
+        let mut val = (0, 0);
+        for _ in 0..24 {
+            self.clock.trigger_and_wait().await;
+            val.0 <<= 1;
+            val.0 |= self.a.is_high()? as u32;
+            val.1 <<= 1;
+            val.1 |= self.b.is_high()? as u32;
+        }
+        // Only implement CH.A, Gain:128 mode
+        self.clock.trigger_and_wait().await;
+        Ok((convert_c24_to_i32(val.0), convert_c24_to_i32(val.1)))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn convert_twos_complement() {
+        assert_eq!(convert_c24_to_i32(0), 0);
+        assert_eq!(convert_c24_to_i32(0x7fffff), 8388607);
+        assert_eq!(convert_c24_to_i32(0x800000), -8388608);
+        assert_eq!(convert_c24_to_i32(0xffffff), -1);
+    }
+}
-- 
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