Input Devices

Either or both temperature inputs to the RoastLogger can be read from any of the following:

1.  A selection of USB HID multimeter/digital thermometers
2.  A selection of serial multimeter/digital thermometers
3.  A roasters display via a webcam and optical character recognition
4.  An Arduino, TC4/C or RL-HT-CTRL providing temperature data via TC4/C, RL-HT-CTRL, Max 6675 or Max 38155
5.  A user supplied application reading users hardware
6.  User hardware communicating temperature data via RS232 serial

In addition to providing the temperature inputs the following devices can provide computer control of a Hottop roaster:

In addition to reading the temperature inputs the following devices can provide computer control of your roasters heater and fan.  These devices require additional hardware to interface to the heater and fan:

  • TC4C
  • Arduino+TC4
  • Arduino + Max 6675 or Max 38155

Please note that I have no financial interest whatsoever in any of these devices except the RL-HT-CTRL board.

If you are considering what device to purchase then it is strongly recommended that you consider the TC4 or TC4C.  The TC4 and TC4C are by far the most flexible devices at a very reasonable price and can be used to provide computer control in addition to temperature logging.

All compatible devices are discussed in more detail below:

1. USB HID devices

You can read from up to 2 of the following devices in any mix (no driver necessary):

  • Victor 86 B multimeter **
  • Victor 86 C multimeter **
  • Tenma 72-7712 (OSX and Windows only - not Linux)
  • Uni-T UT322 (OSX and Windows only - not Linux)

1.1  Victor 86B or 86C multimeters

** A RoastLogger user has recently purchased a Victor 86B multimeter and advises that the manufacturer has recently changed the specification.  Previously these devices communicated via USB HID and were optically isolated from the computer.  The new device is still designated as 86B but is no longer optically isolated from the computer and now communicates by serial not USB HID.  The new devices will, therefore, NOT work with RoastLogger.

I have no information related to the Victor 86C but it may be prudent to assume that it has also been changed.

Anyone considering purchasing either of these multimeters for use with RoastLogger should ensure that they purchase the old USB HID version.  The following photos show the difference in the cable and the connector:

Old USB HID version using optical isolation.  Note the large plastic connector housing the optical isolation and HID communication chip (Note that these versions have always had RS232 stamped into the casing although they communicate by USB HID):
Victor 86B USB HID version

The new serial version which will not work with RoastLogger.  Note this uses a standard USB cable:
Victor 86B RS232 serial version

The following notes relate to the old USB HID version of these multimeters:

This Roast Logger can read temperature data directly from Victor 86 B or Victor 86 C digital multimeters manufactured by Shenzhen Victor Hi-Tech Co. Ltd.   This is the recommended way to interface thermocouples with the RoastLogger.  These devices can be read when the RoastLogger is running in Windows, OS X or Linux.

The Victor 86 multimeters are good quality and low cost (mine cost about 30 GBP including thermocouple) and use a modern optically isolated USB HID (human interface device) interface.

The multimeters are available from ebay and various dealers. If you have difficulty locating them the manufacturer can be contacted at  or their website  and can provide details of local suppliers. 

Victor 86 B & C

The Victor 86 B is considered the most suitable as it displays temperature readings to one decimal place and can be used with standard thermocouples with a miniture two pin plug via an adaptor.  This multimeter, however, displays temperatures in Celsius only.

The Victor 86 C can display results in Fahrenheit or Celsius but only to whole degrees.   A standard adaptor is not available to connect this multimeter to standard thermocouples with a two pin plug.  It is necessary to use the included thermocouple or to use one with separate one pin plugs for each wire.

1.2  Tenma 72-7712 and Uni-T UT322 digital thermometers

If you intend to purchase a device for use with the RoastLogger it is recommended that you purchase one of the above Victor multimeters.  The RoastLogger can, however be used with the Tenma 72-7712 and Uni-T UT322 digital thermometers.  

Please note that, although these devices can read temperatures from two thermocouples, they are NOT capable of sending data on two thermocouples via serial communication.  Due to this two separate devices would be required to send data on two thermocouples.

These devices can be read when the RoastLogger is running in Windows or OS X but not Linux.  

It has been found that the manufacturer of these devices is selling (at least) two different versions of each device.  The different versions use different communication chips and protocols.  Both have exactly the same designation so users can not tell which they are buying.  The RoastLogger now recognises and reads both known versions of these devices.

2. Serial devices

You can read from any one of the following devices (note you must have a suitable driver installed for these devices): 

  • Center 304
  • Center 309
  • Voltcraft K204
  • Maplin N56FU
  • All-Sun EM6000
  • An Arduino, TC4 or TC4C with a suitable sketch providing data on up to two temperatures
  • User hardware using the serial protocol defined in the RoastLogger distribution "User App Connection Info.rtf" file. 

3.  A roasters display via a webcam and optical character recognition

The OCR facilities in this program have been tested and work on many roasters with digital displays but will probably not work on all roaster displays:

In order to achieve reliable readings from a webcam a good clean focused steady webcam image with uniform lighting (no shadows or highlighting in the image) is required. To achieve this the following is ABSOLUTELY ESSENTIAL:-
  • Reasonable quality webcam that can be focused at distances of 10 to 40 cm.
  • Support bracket to hold the webcam steady in relation to the digital    display.
  • A small screen (any uniform colour) positioned so that the reflection the webcam sees in the display is of Nothing but the screen. 

4. Arduino + TC4, TC4C or RL-HT-CTRL

The RoastLogger can also read two temperature inputs from an Arduino, TC4C or RL-HT-CTRL and optionally control the roasters heater and fan.  The RL-HT-CTRL is only for controlling Hottop roasters.  The TC4/C are general purpose and require suitable hardware between the device and the heater/fan.  The TC4/C requires a suitable sketch (software) to communicate with the Roast Logger.  Three sketches are available on the  downloads page and may be used as is or as an example of how to communicate with the Roast Logger to form the basis of your own controller software.   

Arduino sketches are now available on the downloads page for any of the following hardware:

  • Arduino / TC4/C
  • Arduino / MAX 6675 thermocouple interface chips
  • Arduino / MAX 31855 thermocouple interface chips

For information on loading the sketches onto an Arduino or TC4C see the excellent guide by user JackH of

For anyone considering purchasing any of the above I would recommend the TC4/C as it has much greater functionality at a very reasonable price.  It can also be used with other logging software.

Communication with the Arduino or TC4C is possible using either the Arduino Controller, which allows heater power control (and fan control if using the TC4/C) and auto start of logging when the beans are loaded, or the SerialDMMReader (via the DMM tab) which provides a simple interface for reading up to two temperature inputs.

The Arduino Controller and SerialDMMReader work under all the operating systems that the RoastLogger works under, i.e. 32 or 64 bit versions of Windows (XP, Vista or Windows 7), Linux and OS X(64 bit intel based Macs only for OS X, not PowerPC).

Please note that there is an incompatibility, on Linux only, between the Arduino Uno and the RXTX libraries used for serial communication.  This can be permanently fixed by using the updated udev rule included in the distribution.  See the troubleshooting section for details.

A PID and auto tuner was added in version 1.7.6.  Notes on it's use are available here.

5.  A user supplied application reading users hardware

See the following file included in the distribution for details of how to interface your application to the RoastLogger:

/RoastLogger/ReadMe Setup info/User App Connection Info.rtf

6.  User hardware communicating temperature data via RS232 serial

See the following file included in the distribution for details of how to interface your hardware to the RoastLogger:

/RoastLogger/ReadMe Setup info/User App Connection Info.rtf