I’m trying to connect SHT15 digital temperature and humidity sensor to my K8055 board. The problem is however that the sensor uses one line (DATA) for two-way communication. Is it ok to connect the DATA line to both digital input and output of my board at the same time, and SCK line (one-way) to other digital output?
My idea was to set my digital output to 0 when I want to read any inputs from the sensor (otherwise I’d always have 1, as the output and input are connected). But this doesn’t seem to work…
According to the SHT15 datasheet it should be OK to connect both the input and the output of the K8055 to the DATA line.
The problem is that the input circuit of the K8055 limits the high state to about 1.7V.
You have to add a 1k pull-up resistor to the DATA line to get proper voltage to the DATA input of the SHT15.
You need also to add a pull-up resistor to the SCK input of the SHT15.
The outputs of the K8055 are open collector and there is no voltage coming out from these outputs without adding pull-up resistors to the external voltage supply.
Thank you very much for the reply. I’m glad my general idea wasn’t entirely wrong
However I have a couple of other question. The first and the most important is - what are the chances that I damaged the sensor by trying to connect DATA and SCK lines directly to the K8055 board without any resistors?
I tried to read a little about pull-up resistors, but I must admit that they are way above my level of experience… Wouldn’t you mind drawing a sketch or describing how exactly should I connect the sensor, resistors, etc?
Ok, the other problem was - I used some old (2003) datasheet for the sensor. Now I found a newer one (2010) which includes a diagram with pull-up resistor.
The sheet says the pull-up resistor should be 10k, not 1k. Is that correct? And do I use the same power supply as VDD for the sensor and DATA line via pull-up resistor?
[quote]The sheet says the pull-up resistor should be 10k, not 1k. Is that correct?[/quote]The input of the K8055 can be properly pulled up with 1k resistor. If you use 10k, then the high state of the K8055 input will be about 2.4V. This may be too low for the sensor input to detect it as “high” state.
According to the datasheet the maximum output current of the SHT15 is 4mA. You can use a pull-up resistor 1.5k or higher value.
[quote]And do I use the same power supply as VDD for the sensor and DATA line via pull-up resistor?[/quote]Yes.
Is it normal to have 0.6V between digital outputs (at the time when they are 1) and ground? Can this be the reason I always have a bit less than 3.3V (voltage of my external power supply) on my output after pull-up?
[quote]Is it normal to have 0.6V between digital outputs (at the time when they are 1) and ground?[/quote]Yes, this is normal. This amount of voltage remains over the output transistor when conducting.
Can I use several different voltage sources on separate digital outputs? I’d like to use 12V for my relay and 5V for the temperature sensor (which I’m still struggling to get to work).
[quote]Can I use several different voltage sources on separate digital outputs? I’d like to use 12V for my relay and 5V for the temperature sensor[/quote]Yes, you can in this case. Connect the +12V to the CLAMP terminal. Connect the relay coil between the CLAMP terminal and the digital output.
Connect the temperature sensor inputs to other digital outputs. Add some resistors between these terminals and the +5V to act as “pull-up” resistors for these output terminals.
