![]() How you control those control pins is of course up to you – either with some digital logic circuit for your application or as mentioned earlier with a microcontroller.Īpart from the power supply requirements, there are a few limitations to keep in mind. For example, to select pin 9 (9 in binary is 1001) you set the IC pins S0 and S3 to HIGH, and S1 and S2 to LOW. If you scroll down a bit hopefully you noticed that the combination of S0~S3 is in fact the binary equivalent of the pin number – with the least significant bit first. nothing) it shows what combination of HIGH and LOW for the control pins are required to select which I/O pin the current will flow through. Not only does it show what happens when pin 15 is set to HIGH (i.e. So how does that work? Once again – reach for the the data sheet and review the following table: By setting these HIGH or LOW (Vcc or GND) you can control which I/O pins the current flow is directed through. Finally there are the four control pins – labelled S0~S3. ![]() The sixteen inputs/outputs are labelled I0~I15. This is where the current either flows in to be sent to one of the sixteen outputs – or where the current flows out from one of the sixteen inputs. You can always control this with a digital output pin if required, or just tie it to GND if this doesn’t matter. Pin 15 is used to turn the control the current flow through the inputs/outputs – if this is connected to Vcc the IC stops flow, and when connected to GND it allows flow. The power supply for the part is applied to pin 24, and GND to … pin 12. ![]() Next – consider the pinout diagram from the data sheet: If for some reason you have the 74 HCT4067 it can only work on 4.5~5.5V DC. The first thing to note is that the 74HC4067 can operate on voltages between 2 and 6V DC, which allows use with 3.3V and 5V microcontrollers and boards such as Arduino and Raspberry Pi. Another way to think abou it is that you can consider the 74HC4067 to be a digital replacement to those rotary switches that allow you to select one of sixteen positions.ĭon’t let that put you off, it’s just what we had in stock at the time. The part itself is available in through-hole and surface mount versions.Īt this point you should download the data sheet, as we refer to it through the course of the article. That’s a mouthful – however in simple form it’s an IC that can direct a flow of current in either direction from one pin to any one of sixteen pins. One example of this is the 74HC4067 16-channel analog multiplexer demultiplexer. The board also breaks out the chip’s “enable” pin, which when driven high, will completely disconnect the common pin (all switches “off”).Now and again there’s a need to expand the I/O capabilities of your chosen microcontroller, and instead of upgrading you can often use external parts to help solve the problem. The internal switches are bidirectional, support voltages between ground and VCC, have low “on” resistance and low “off” leakage, and to prevent crosstalk, perform “break-before-make” switching. By using multiple boards, you can create similar arrangements for I2C, SPI, etc. If you want two-way communications, you can add a second board to route your microcontroller’s TX line to 16 device’s RX lines. You can then select any one of those 16 devices to listen to. For example, you could use it to connect the TX pins of 16 devices to one RX pin on your microcontroller. Since the mux/demux also works with digital signals, you can use it to pipe TTL-level serial data to or from multiple devices. This allows you to connect up to 16 sensors to your system using only 5 pins! To control it, connect 4 digital outputs to the chip’s address select pins (S0-S3), and send it the binary address of the channel you want (see the datasheet for details). ![]() It works with both digital and analog signals (the voltage can’t be higher than VCC), and the connections function in either direction. This chip is like a rotary switch - it internally routes the common pin (COM in the schematic, SIG on the board) to one of 16 channel pins (CHANxx). This is a breakout board for the very handy 16-Channel Analog/Digital Multiplexer/Demultiplexer CD74HC4067. ![]()
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