Initial commit.

.gitignore

@@ -0,0 +1,4 @@
+*~
+/temper
+/temper-*
+

Makefile

@@ -0,0 +1,11 @@
+temper: temper.c
+	@gcc $< -l hidapi-hidraw -o $@
+
+release: temper
+	@cp temper temper-linux-$$(git tag -l --points-at HEAD | cut -d/ -f2)-$$(uname -m) \
+		&& strip temper-linux-$$(git tag -l --points-at HEAD | cut -d/ -f2)-$$(uname -m) \
+		&& sha256sum temper-linux-$$(git tag -l --points-at HEAD | cut -d/ -f2)-$$(uname -m) > temper-linux-$$(git tag -l --points-at HEAD | cut -d/ -f2)-$$(uname -m).sha256sum
+
+clean:
+	@rm -f temper temper-* *~ .*~
+

README.md

@@ -0,0 +1,45 @@
+# Read the temperature of a TEMPer device with ID 413d:2107
+There are many libraries (C, Python) out there for reading the TEMPer
+family of thermometer and hygrometer devices.
+
+Since I own only one device with USB ID `413d:2107` and wanted just simple JSON output, I
+wrote yet another program to read from this kind of USB device.
+
+## Dependencies
+It uses the [HIDAPI](https://github.com/signal11/hidapi) library as dependency.
+
+On Debian (based):
+
+    sudo apt install libhidapi-hidraw0
+
+On Arch:
+
+    sudo pacman -S hidapi
+
+## Device
+
+### `dmesg`
+
+Example `dmesg` output:
+
+    [35813.492854] usb 2-1.3: new full-speed USB device number 25 using ehci-pci
+    [35813.591045] usb 2-1.3: New USB device found, idVendor=413d, idProduct=2107, bcdDevice= 0.00
+    [35813.591053] usb 2-1.3: New USB device strings: Mfr=0, Product=0, SerialNumber=0
+    [35813.603164] input: HID 413d:2107 as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/0003:413D:2107.0027/input/input39
+    [35813.660537] hid-generic 0003:413D:2107.0027: input,hidraw0: USB HID v1.11 Keyboard [HID 413d:2107] on usb-0000:00:1d.0-1.3/input0
+    [35813.662589] hid-generic 0003:413D:2107.0028: hiddev1,hidraw1: USB HID v1.10 Device [HID 413d:2107] on usb-0000:00:1d.0-1.3/input1
+
+### `lsusb` 
+
+Example `lsusb -d 413d:2107` output:
+
+    Bus 002 Device 025: ID 413d:2107
+
+### Photo
+
+Photo of my TEMPer device:
+
+![](TEMPer_413d_2107.jpg)
+
+## License
+The program is licensed under [GPLv3](https://www.gnu.org/licenses/gpl-3.0.txt) ([local copy](LICENSE-GPL-3.0.txt)).

temper.c

@@ -0,0 +1,96 @@
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <hidapi/hidapi.h>
+
+#define MAX_STR 255
+
+char* find_device_path(unsigned short vendor_id, unsigned short product_id);
+bool read_temperature(hid_device *handle, int* result);
+
+#define TEMPer_VendorId 0x413d
+#define TEMPer_ProductId 0x2107
+
+int main(int argc, char* argv[]) {
+  if(hid_init()) {
+    fwprintf(stderr,L"failed to initialize HID API\n");
+    return EXIT_FAILURE;
+  }
+
+  char* path = find_device_path(TEMPer_VendorId, TEMPer_ProductId);
+
+  if(!path) {
+    fwprintf(stderr,L"cannot find matching HID device ID %x:%x, try 'lsusb' or 'lsusb -d %x:%x'\n",
+             TEMPer_VendorId,TEMPer_ProductId,
+             TEMPer_VendorId,TEMPer_ProductId);
+    return EXIT_FAILURE;
+  } else {
+    hid_device *handle =  hid_open_path(path);
+
+    if (!handle) {
+      fwprintf(stderr,L"failed to open device %s\n"
+               "to avoid running this program as root, put the following udev rule in e.g. /etc/udev/rules.d/90-temper.rules\n\n"
+               "SUBSYSTEMS==\"usb\", ACTION==\"add\", ATTRS{idVendor}==\"%x\", ATTRS{idProduct}==\"%x\", MODE=\"666\"\n\n",
+               path,TEMPer_VendorId,TEMPer_ProductId);
+      free(path);
+      return EXIT_FAILURE;
+    }
+
+    int temperature = INT_MIN;
+    if(read_temperature(handle,&temperature)) {
+      printf("{ \"temp_celsius\": %d.%d }\n",temperature/100,temperature%100);
+    }
+    hid_close(handle);
+    free(path);
+  }
+
+  if(hid_exit()) {
+    fwprintf(stderr,L"failed to shutdown HID API\n");
+    return EXIT_FAILURE;
+  }
+  return EXIT_SUCCESS;
+}
+
+bool read_temperature(hid_device *handle, int* result) {
+  unsigned char buf[16];
+  unsigned char cmd[8] = { 0x01, 0x80, 0x33, 0x01, 0x00, 0x00, 0x00, 0x00 };
+
+  memset(&buf,0,sizeof(buf));
+
+  int rc = hid_write(handle, cmd, sizeof(cmd));
+
+  if(-1 == rc) {
+    return false;
+  }
+
+  // expected response is exactly 8 bytes
+  bool ok = (8 == hid_read(handle, buf, sizeof(buf)));
+
+  if (ok) {
+    // temperature is stored in byte 2&3 => return value is a hundreth of °C
+    *result = (buf[2]*256 + buf[3]);
+  }
+  return ok;
+}
+
+
+char* find_device_path(unsigned short vendor_id, unsigned short product_id) {
+
+  struct hid_device_info *devices = hid_enumerate(vendor_id,product_id);
+  struct hid_device_info *cur_dev = devices;
+
+  while (cur_dev) {
+    // the hardware provides two devices, we need the second one
+    if (1 == cur_dev->interface_number && cur_dev->path) {
+      char* path = malloc(strlen(cur_dev->path)+1);
+      strcpy(path,cur_dev->path);
+      hid_free_enumeration(devices);
+      return path;
+    }
+    cur_dev = cur_dev->next;
+  }
+  hid_free_enumeration(devices);
+  return NULL;
+}