Add conversion function for resistance to temperature conversion and add it to thept command of the shell

stm-firmware/include/reflow-controller/temp-converter.h

@@ -0,0 +1,31 @@
+/* Reflow Oven Controller
+ *
+ * Copyright (C) 2020  Mario Hüttel <mario.huettel@gmx.net>
+ *
+ * This file is part of the reflow Oven Controller Project.
+ *
+ * The reflow oven controller is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * GDSII-Converter 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GDSII-Converter. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __TEMP_CONVERTER_H__
+#define __TEMP_CONVERTER_H__
+
+/**
+ * @brief Convert PT1000 resistance to temperature in degrees celsius
+ * @param resistance PT1000 resistance value
+ * @param[out] temp_out Temperature output
+ * @return 0 if ok, -1 if value is below conversion range, 1 if value is above conversion range,-1000 in case of pointer error
+ */
+int temp_converter_convert_resistance_to_temp(float resistance, float *temp_out);
+
+#endif /* __TEMP_CONVERTER_H__ */