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hacking_an_eq-3_model_n [2016/03/21 22:41] – [How the Model N Works Inside] Photo section. Traumflug | hacking_an_eq-3_model_n [2018/05/27 16:10] (current) – external edit (unknown user) | ||
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The **[[http:// | The **[[http:// | ||
- | ===== How the Model N Works Inside ===== | + | ===== How the Model N Looks Inside ===== |
Here are a few pictures from inside the device. After pulling out the dial wheel on the front (it's a snap requiring some force) and removal of 4 Torx screws found under the battery hatch it can be taken apart easily. | Here are a few pictures from inside the device. After pulling out the dial wheel on the front (it's a snap requiring some force) and removal of 4 Torx screws found under the battery hatch it can be taken apart easily. | ||
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+ | ==== Actuator Motor ==== | ||
+ | |||
+ | A simple DC motor running on full battery voltage, which is about 3.2\_volts. At motor start, voltage is 100% PWM for a few milliseconds, | ||
+ | |||
+ | Current consumption without load is about 13\_mA. With gears fully blocked it can go up to 40\_mA, but then some overload protection kicks in. Looks like motor current detection is used as kind of endstops to find absolute position of the drive. During initial calibration the Model N moves as far as it can in both directions. | ||
+ | |||
+ | On the left side of the PCB a number of parts hint on a H-Bridge. Actuator motor is connected with the black and red wire soldered onto the board. | ||
+ | |||
+ | ==== Circuitry ==== | ||
+ | |||
+ | At the center one can see the dial wheel encoder. Two big solder points for mechanical fastening, three blobs of solder bottom left of the center for the encoder signal. | ||
+ | |||
+ | Microprocessor (MCU) is a STM8L052C6 (8-bit\_CPU, | ||
+ | |||
+ | Mechanical buttons //TA1//, //TA2//, //TA3// for the user interface. TA2 is for the dial wheel, which can be pressed. | ||
+ | |||
+ | ==== Temperature Sensor ==== | ||
+ | |||
+ | Temperature sensor of the device is a 10\_kOhms thermistor. It's //R4// at the bottom center. Yes, it's SMD, so it likely measures more PCB temperature than room temperature. | ||
+ | |||
+ | Measuring the thing isn't trivial, because it isn't supplied with voltage most of the time. It's a battery supplied device, after all, so wasting a mA or two all the time is indeed not a good idea. BTW., the Model N refuses to pick up normal operations without a successful calibration movement, so you have to mount it on an actual radiator valve at least once. | ||
+ | |||
+ | It looks like the thermistor is connected via //R5// to pin\_32 of the MCU. Looking at the STM8L052 data sheet, this is about the only pin which makes sense. | ||
+ | |||
+ | ==== Measurement Points ==== | ||
+ | |||
+ | There are several measurement points located on the PCB. These appear to be: | ||
+ | |||
+ | //MP1//: Menu key. Zero volts pressed, else 3\_volts. | ||
+ | |||
+ | //MP2//: Dial wheel key. Same behaviour as MP1. | ||
+ | |||
+ | //MP3//: Thermistor voltage. To measure the thermistor one can measure between MP3 and MP6 with an ohms meter. | ||
+ | |||
+ | //MP4//, //MP5//: Dial wheel encoder signal. | ||
+ | |||
+ | //MP6//: Ground. Maybe pointless, but it's just GND. | ||
+ | |||
===== Goal of the Hack ===== | ===== Goal of the Hack ===== | ||
- | One of the drawbacks of this model is the temperature sensor built right into the housing. As such it measures not general room temperature, | + | One of the drawbacks of this model is the temperature sensor built right into the housing. Openings for ventilation are really tiny. As such it likely |
- | Everything electronic? Heck, then let's rip the sensor out and connect it back with a pair of long wires. This way, temperature can be measured anywhere. Sounds easy, right? With some soldering skill it is! | + | Everything electronic? Heck, then let's rip the sensor out and connect it back with a pair of long wires. This way, temperature can be measured anywhere. Sounds easy, right? With some soldering skill it pretty much is! |
===== The Hack in Pictures ===== | ===== The Hack in Pictures ===== | ||
- | During the modification a lot of pictures were taken, so let these speak. | + | During the modification a lot of pictures were taken, so let' |
- | | picture | + | | {{ : |
+ | | {{ : | ||
+ | | {{ : | ||
+ | | {{ : | ||
+ | With all this done, the Model N works just as before, just room temperature can be measured on a more meaningful position. | ||
===== How the Result Works ===== | ===== How the Result Works ===== | ||
- | The modification turned out to work just fine. After confirming this the thermistor wasn't mounted in the room somewhere, but connected directly to the ISTA consumption counter of the radiator. And the Model N didn't like this, the valve fully opened and closed every few minutes. For whatever reason. Hard to say, because it's Closed Source, so reprogramming the microprocessor wasn't a realistic option. | + | The modification turned out to work just fine. After confirming this, the thermistor wasn't mounted in the room somewhere, but connected directly to the ISTA consumption counter of the radiator. And the Model N didn't like this, the valve fully opened and closed every few minutes. For whatever reason. Hard to say, because it's Closed Source, so reprogramming the microprocessor wasn't a realistic option. |
This eventually led to development of the [[ISTAtrol]], | This eventually led to development of the [[ISTAtrol]], | ||
hacking_an_eq-3_model_n.1458596500.txt.gz · Last modified: 2018/05/27 16:10 (external edit)