From e94601f54feb5c1106ebf9adf6fc8c59316a6de1 Mon Sep 17 00:00:00 2001
From: topquark12 <aw@m-labs.hk>
Date: Tue, 29 Dec 2020 17:09:03 +0800
Subject: [PATCH] pid: fix derivative calculation

Reviewed-on: https://git.m-labs.hk/M-Labs/thermostat/pulls/40
Co-Authored-By: topquark12 <aw@m-labs.hk>
Co-Committed-By: topquark12 <aw@m-labs.hk>
---
 src/pid.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/pid.rs b/src/pid.rs
index 176283c..6001c54 100644
--- a/src/pid.rs
+++ b/src/pid.rs
@@ -85,7 +85,7 @@ impl Controller {
             None =>
                 0.0,
             Some(last_input) =>
-                f64::from(self.parameters.kd) * (input - last_input) / time_delta,
+                f64::from(self.parameters.kd) * (last_input - input) / time_delta,
         };
         self.last_input = Some(input);