How to create an electronic 3P3T switch? - Page 1
Forum section: electronics / beginners

author: mdijkens
author_rank: Regular Contributor
timestamp: April 11, 2018, 10:36:26 pm
content: HiI want to replace a 3 pole 3 throw latching on-off-on switch (see attached) with electronics to switch it with a mcuall 3 poles are only used for small ttl signals, but I don't want to use mechanical relaysit would be nicest if it is a scalable design that could also be used if I want to switch 5 or 10 signalsI have been googling for sometime now, but can't really find a nice (hopefully) not to complex solutionWhat would be a good way to implement this? are there ic's that do stuff like this? Any schematics that could point me in the right direction?I assume this requirement pops up regularly in designs where you electronically need to switch multi-line inputs/outputs?

author: Ian.M
author_rank: Super Contributor
timestamp: April 11, 2018, 11:11:01 pm
content: Google: Crosspoint switch ICIts up to you to code the MCU controlling it to make the correct connections between inputs and outputs.You could also do it with some CD4051 or CD4052 analog switches, (or their 74HC equivalents), with their control inputs in parallel. 4051 is 1P8W and 4052 is 2P4W.http://www.ti.com/lit/ds/symlink/cd4051b.pdfN.B. for 'latching' you'd have to maintain control circuit state. i.e. if its to power back up in the same state your MCU need some non-volatile or battery backed memory

author: mdijkens
author_rank: Regular Contributor
timestamp: April 11, 2018, 11:50:25 pm
content: Thanks for pointing me in the right direction!I looked at the datasheet and the CD4053 seems to be exactly what I'm looking forSee attached picture:Could it work like this?Assuming MCU and both UARTs all use 3V3 or 5V and the UARTs do not consume more than 30-40mA ?Could I just duplicate this for 6, 9, ... poles?

author: Ian.M
author_rank: Super Contributor
timestamp: April 12, 2018, 12:31:04 am
content: Nope. The 4053 is no good for directly switching power.Personally I'd use a 4052 for the signal lines and P-MOSFETs (with gate-source pullup resistors so they are normally off) as high side switches to control power to the two UARTs. IF you use a 74HCT4052, its inputs are 3.3V compatible when its running with 5V Vcc, so no level conversion required.If you can rearrange the circuit to have one active high MCU output to enable each UART, rather than having IO2 as a master enable and IO1 selecting the UART it would make it much easier as then you could useAO6602complimentary MOSFETs, with its N-MOS device as a level shifter driving the gate of its P-MOS device so the MCU can control a supply voltage greater than its logic '1' level. Alternatively, if there is a higher unregulated rail available, simply use a separate regulator with an enable pin for each UART.Alternatively, keep the 4053, (use the 74HCT version to avoid the need to use level shifters), and use its third channel to switch ground to the gate of one of the high side P-MOSFETs at a time to switch on that UART. To extend it up to 16 ways, use three74HCT4067chips, for the RX, TX and Vcc gate control, and 16 P-MOSFETs and gate pullup resistors.

author: TomS_
author_rank: Frequent Contributor
timestamp: April 12, 2018, 02:12:26 pm
content: Ive used 405X's (TI CD74HCT4052's most recently) in a couple of projects. Just dont forget to connect the VEE pin and they are very useful for switching signals around between devices.In one project I used them to select the UART of N devices, and in another I switch CLK and MISO for SPI like devices (actually shift registers - MOSI is connected to all devices permanently, as without a CLK input the change in levels on the input pin is ignored).Also remember to pull up or down the signals connected to which ever side becomes the "output" of the 405X as I dont believe they are complementary outputs, and consequently any inputs on that signal would float otherwise.