level-shiftinglogic-levelserial
I have a sensor which constantly outputs serial data at very low voltages (in the milli-volt range), however I need to read this serial data using a PIC micro controller. How can i convert this data to logic level using basic components.
All solutions i have read so far are for bi-directional communication and require a specialized chip. For my purposes I simply require uni-directional communication, and would prefer used basic components available at any electronics stores.
An opto-coupler (or two) could easily do the job, and will provide some welcome isolation between the two devices if the power supplies should float apart. If you don't know why this is a good idea, you really should read up about it.
We have run opto-couplers at MHz, even passed PAL video through them, so a low-speed data bus will be fine.
Without looking too closely, I'd guess that a popular part such as 4n25 would be entirely adequate.
It's likely because usually the designer is specifying the two supply voltages and they are thus known a priori. Since there is likely a cost in performance and/or die size to making a symmetric level converter, the majority of the market can be well served by types with specified Vcca > Vccb or whatever. For example, the common bidirectonal level conversion method using a discrete MOSFET (from here):
..will not work if you swap the supply voltages.
There are available converters with symmetric supply voltage limits, for example, the TI TXB0304, which could come in handy if you needed to program the supply voltage or have it supplied externally in order to deal with customer requirements (the alternative might be to operate all your circuitry at the lowest or highest voltage possible, or to use two converters and similarly set an intermediate supply voltage).
Best Answer
Base on the oscilloscope's response you can't be sure of the actual protocol of the sensor and you should watch up the sensor's datasheet. The sensor can be analog or its output can be based on current and not voltage in the case you can use any kind of current sensor or many other techniques.
It is hard to offer the exact answers to the question due to lack of information. Any way there are several techniques which you can use to fulfill your purpose regarding to the relative frequency and variation of the voltages. First you can use the micro's ADC of course if the frequency is low enough. Also you can use transistor or high slew rate op-amp to read your signals. If you determined the signal's frequency and its voltage variation (if there is any) and the sensor's output's type, there could be more available answers.