Choosing a switch for DC signals of small current - Page 1
Forum section: electronics / beginners

author: takeda
author_rank: Newbie
timestamp: November 24, 2015, 06:23:08 pm
content: Hi all,I need to create a board with a lot of switches. That switches will control some jumpers on a development kit for a microcontroller (there is no need to say something specific about this).Consider that the development kit has some 2-pin headers that when connected (short circuited) with a jumper they configure the kit.Typically they are all pulled up 3.3V lines that are grounded when short circuited.I need to create a board that will control the development kit's pin headers so that I can create a set of different configurations for the jumpers.This is required because I need to run nightly acceptance tests for the DK, during which the jumper configuration changes (from test to test)But enough with this. A am mostly a software engineer, I know how to use a relay, the basic BJT configurations but I can't make a decision on thissince I need a lot of switches (let's say 40) that will be controlled by a microcontroller (and some extra digital circuitry accessories)Any ideas on what to choose for this switch?Should I use miniature smd relays (which is the easiest but very expensive and space consuming)?Could I use optocouplers as a DC switch for low current? (<1mA) Anything else?Can I use analog switches such as dg9431?Thanks

author: Jeroen3
author_rank: Super Contributor
timestamp: November 24, 2015, 06:39:09 pm
content: Buy more development kits. (fastest)A switchmatrix all depends on the functions of the pins. Are these fully digital, or do they share analog for some features or maybe open drain like i2c.

author: takeda
author_rank: Newbie
timestamp: November 24, 2015, 06:41:20 pm
content: This is impossible since I have more than 20 configurations per test suite. Anyway, consider this impossible.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: November 24, 2015, 06:42:05 pm
content: Quote from: takeda on November 24, 2015, 06:23:08 pmIs that always the case? If so there's no need for switches/relays at all, you should be able to just drive them directly from a 3.3v GPIO (or shift register or similar). You could also use Nch FETs to pull the 3.3v side down to ground.

author: takeda
author_rank: Newbie
timestamp: November 24, 2015, 06:49:57 pm
content: Yes you are right, I can use a shift register and drive from the output of this ensuring there is a protective in series resistor.Yes this is always the case, some pulled up lines to Vcc (where VCC is typically 3.3V). There are some leds also on the board controlled by a jumper but I don't need to control them electronically.Thanks

author: takeda
author_rank: Newbie
timestamp: November 24, 2015, 07:43:49 pm
content: I have been naive, I am sorry for the misleading information. The jumper configuration regards connections between a microprocessor's pinsto external lines like UART pins of an FT232 chip.Let's say it's a Atmel 8bit proc on side and an ft232 chip on the other and some jumpers connectAVR's PinB0 --> FTDI UART TXAVR's PinB1 --> FTDI UART RXsomething like that for all pins. No pulled up lines in any case (except just for the reset line)I think I will go with miniature relays, 16 per development kit.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 24, 2015, 07:57:04 pm
content: Is it this board perhaps?https://www.embeddedartists.com/products/lpcxpresso/xpr_base.phpIt has the highest count of selection jumpers I've ever seen. And that includes that some switches operate muxes and buffers.

author: takeda
author_rank: Newbie
timestamp: November 24, 2015, 08:22:14 pm
content: No it's not. I would prefer to not say. Sorry

author: Simon
author_rank: Unknown
timestamp: November 25, 2015, 07:37:27 am
content: You can get electronicly controlled analogue switches.