Questions tagged [expander]

Questions regarding Port or IO Expanders, be it I2C, SPI, 1-Wire, serial/uart or similar. Shift-Registers are normally NOT considered Expanders, and have their own tag.

Filter by
Sorted by
Tagged with
1 vote
6 answers
157 views

Should I connect the base of a 5 V high-side PNP to a 3.3 V GPIO IC?

I'm trying to drive a 5V 200mA fan from a PCF8574 powered by 3.3 V. For context, I asked a separate question about using active low vs high on this expander, and @Justme recommended using a high-side ...
  • 1,781
1 vote
3 answers
69 views

Is active HIGH or LOW preferred for driving loads with the PCF8574?

I'm switching a 5V 200mA case fan with a PCF8574. Since this expander is best used as a current sink (it can sink 25mA, but I think it can only supply something like 300uA), I supposed that a PNP ...
  • 1,781
3 votes
1 answer
136 views

Is it advisable to current sink an LED sourced from 5V into a PCF8574 sourced from 3V3?

I'm using a PCF8574 to sink current from an LED. The PCF8574 VDD is 3V3, but the LED is sourcing from 5V. I think voltage drop on the LED is around 2V, so if I understand correctly, then the IO IC ...
  • 1,781
4 votes
1 answer
258 views

Why does read from I2C GPIO Expander MCP23017 requires NACK

I'm using the MCP23017 16-bit I2C GPIO Expander in combination with the microcontroller PIC18F47J53. Both products are from Microchip. Datasheet MCP23017 Datasheet PIC18F47J53 I use MCC (MPLab Code ...
0 votes
4 answers
112 views

I2C Strange goings on

I am using a Teensy 4.0 and an MCP23016 Port Expander (only I2C device) on my PCB. I have 4k7 pullups to 3V3 on SDA & SCK. SCK track is 77.9 mm long, 0.254 wide. SDA 64.3 mm long, 0.254 wide. I ...
0 votes
2 answers
156 views

Port expander with high side switch ground dilemma

I have a design wherein the basic idea is to control individual LED strings and dim (analog dimming) them using Pi Pico via I2C interface. This board is the LED driver which will be connected to the ...
4 votes
3 answers
458 views

EEPROM with GPIO [closed]

Trying for a while now, but I cannot find an EEPROM memory with some address bit mapped to a GPIO. Or from a different angle, a GPIO expander with an EEPROM memory to save the config. Do such devices ...
0 votes
1 answer
162 views

individual tri-state output IC with SPI / I2C / shift register input

Is there any simple non-MCU IC that allows switching several outputs (8 or more) tri-stated, eg. set any output to either high (~2V), low or open individually ? Input may be shift-register, SPI or I2C....
  • 541
0 votes
1 answer
244 views

How do you configure the 74HC595 to have low pin outputs at power on?

So far I have somewhat successfully used a shift register (74HC595) and an output expander (PCF8574) to control FETs and BJTs. The main drawback so far seems to be that the chips I’m using have ...
  • 1,781
0 votes
1 answer
258 views

Driving MFET with IO Expander ( mcp23008/mcp23017)

for my project I want to drive about 12 x IRLl014 FETs with an ESP32. To get more pins I want to put a IO-expander, either a MCP23017 or MC23008 onto the I2C and out onto the gate. I know that driving ...
  • 191
1 vote
2 answers
272 views

Daisy chain multiple PCB with an existing IDC cable

I'm not sure, if I just miss the obvious, but I'm stuck on seemingly simple problem and can't find a solution. I have a series of PCBs, I want to daisy chain. The number is between 8 and 12(max). The ...
  • 1,762
2 votes
0 answers
67 views

Using an MCP23008 IC with a 4X4 matrix keypad on a Raspberry Pi [closed]

I want to be able to free up the native GPIO pins on my Raspberry Pi Zero. I know the MCP23008 gives me 8 extra pins, but I can't seem to find any resources on using the additional pins with a 4X4 ...
0 votes
1 answer
57 views

Can I/O expanders be used to drive a Camera or LCD?

After searching around it seems that I/O expanders are used mostly to drive LEDs or buttons. Could something more complicated like an LCD be driven without bit banging? I.e. are there typically ...
  • 1
0 votes
1 answer
111 views

MCP23S17 - do I have to use both Chip Select and Hardware Addressing?

I've used MCP23S17 before. 6 of it and I just used Chip Select. Hardware address pins all 0. https://ww1.microchip.com/downloads/en/DeviceDoc/20001952C.pdf In datasheet, hardware addressing can be ...
1 vote
2 answers
920 views

Feedback schematic/pcb 16 channel relay wifi module

I have a few questions about a 16 channel relay module I designed, maybe someone can help me. Generally this consists of a ESP-12F, two I2C IO Expander, two darlington array ICs to drive 16x 5V relays....
0 votes
2 answers
378 views

74HC595 getting really hot on my pcb

I've designed a fairly simple circuit with some shift registers (3 output en 1 input). In the circuit, I've connected the inputs from the input shift register to pin connectors on the board (so I ...
0 votes
3 answers
181 views

Finding a I/O expander that supports 18 PWM outputs or another solution for MOSFET control

I am a student working on a university project. I need help figuring out how I can supply 18 PWM signals to 18 gate drivers, in a 3-phase inverter. The inverter is built up of 3 half bridges, with 6 ...
  • 13
0 votes
1 answer
114 views

Does a Mcp23s17 output pin keep the value after being unselected?

I'm designing a SPI based communiations circuit between Raspberry Pi4+B as a master and (n x 8) GPIO expander modules, as slaves. Concretely we have selected an MCP23S17 GPIO expander: Datasheet By ...
  • 705
0 votes
0 answers
224 views

PCF8574 and OLED SSD1306 I2C conflict

I have a ESP12 module which is connected to multiple I2C devices such as an 24C08 EEPROM, DS1307 RTC and a PC8574 expander. Everything works fine until I decided to add an OLED module to this setup. ...
0 votes
0 answers
332 views

Driving laser modules with MCP23017 and MOSFETs

I would like to make a PCB to switch 16 laser modules on and off. The laser module in question is this one: https://www.sparkfun.com/products/9906 I believe the module already has a driver included (...
  • 15
0 votes
1 answer
207 views

Use PCF8574 switch selection multiple SPI slave devices, is it possible?

My project use esp8266's SPI communicate with MCP3208 and SDCard, to select which device to be communicated, that device's CS pin need to set low, and set high to another device to disable, right? My ...
0 votes
1 answer
156 views

Trouble with SO on MCP23S18 spi gpio expander

I am unable to get a signal out of the slave out (SO) line of an MCP23S18 For those not familiar it is a slave SPI gpio expander. Clocking in 32 bits, as it goes 16 bits set up, 8 bit opcode, 8 bit ...
  • 161
1 vote
2 answers
342 views

Is this a valid configuration for decoupling capacitors on an IC with two supply pins?

I have a project that's using an IC that only comes in SMD packages. With my limited soldering experience, I think I could potentially solder a TSSOP, but I think QFN is well beyond my capabilities. ...
1 vote
5 answers
2k views

Why are devices like the MCP23008 or PCF8574 still around when cheaper alternatives exist? [closed]

INB4: if this question doesn't fit this board, please delete. But I don't know where else to ask. There're plenty of I/O port expanders available. Most of them add 8 I/O lines at the cost of two I2C ...
  • 591
3 votes
5 answers
3k views

UART expander (5 ports to 11 ports)

I have a board that I would like to design and there are 11 devices that can only be spoken to via UART. I am restricted to a Microchip uC chip product range and I have found one with 5 UART ports. I ...
  • 369
1 vote
1 answer
168 views

Pull up/down a pin on a PCA9536 does not register?

Quite a obscure question here, concerning a very specific I2C expander IC, however I believe that this example can be replicated with most expander bus ICs. I am using a PCA9536 to switch the 4 pins ...
  • 13
0 votes
3 answers
187 views

Volt/Amp dependent RLC band pass -> Loudspeaker expander using lightbulbs

I want to create a input energy dependent frequency shunt network, which goes in parallel with a loudspeaker, At low volumes, a certain midrange frequency should be shunted off the loudspeaker. The ...
0 votes
2 answers
3k views

Wiring CJMCU-2317 MCP23017

I got the CJMCU-2317 MCP23017 I2C Serial Interface 16 bit I/O Expander Serial Module to use on a split keyboard as an extension matrix. This seems like an all-in-...
2 votes
3 answers
575 views

Controlling 13 outputs with a mcp23017 or 74hc595 and two uln2003?

I need to drive 13 20ma (constant) loads with a single microcontroller with only 5 available pins. My first thought was to just use a mcp23017 or some 74hc595's but after reading the datasheets it ...
0 votes
2 answers
3k views

Multiple analog inputs on A0 pin (ESP nodemcu) with PCF8574

I am trying to read out several analog values on one analog input on the nodemcu. As sensors I am using two potentiometers which are connected to GND via a PCF8574 8-bit I/O expander. With the code ...
  • 1
0 votes
1 answer
78 views

Power supply issues with LCD and MPC23017 expander chips

I have an Arduino Uno and I'm working on a project that requires me to use six MCP23017 chips on a I2C bus plus a LCD 16x2 monitor. I need MCP23017 chips to power 36 LED's at the same time (8 LED's ...
  • 3
1 vote
1 answer
6k views

Are pull-up resistors needed when connecting buttons to a IO expander?

I'm connecting many momentary switches to a IO expander, like the MCP23017: . I read that I need to put pull-up resistors for each switch connected to the MCP23017. On another place (datasheet), I ...
  • 1,752
0 votes
1 answer
642 views

Will continuously polling I2C port expander damage it or reduce its life?

I am using I2C port expanders namely TCA9554A and TCA6424A in my project. I have two options to read the inputs - (a) wait for interrupt and read (b) continuously keep polling the chip for any input ...
  • 7,656
1 vote
2 answers
335 views

Benefits of using an External A/D converter with ATmega128

I am new to electronics and working on my first project. Can someone explain why you would use an external A/D converter instead of the on board one? According to Mplabs the ATmega128 has a 8-...
0 votes
2 answers
166 views

How to expand a pulse by a factor

i have a read out ic of optical front end which gives out digital pulse(0-3.3V) of width 10ns to 150ns repeating at a rate of 1Hz-70KHz i have to measure the pulse width, but it needed a high end ...
  • 672
4 votes
2 answers
1k views

MCP 23018/23S18 for LED and Switch control

I'm working on a project that involves about 200 LEDs and about 120 Switches. I'd like to use several MCP23S18 DIP chips across 2-3 buses to control everything. I'm a CS guy and just want to make sure ...
1 vote
2 answers
719 views

Should the reset pin on MCP23S17 go to a GPIO?

Most example schematics for Arduino, Raspberry Pi etc have the reset pin tied to GND. If number of GPIOs on the MCU wasn't a problem, would it be beneficial to have the reset of the expander ...
1 vote
2 answers
778 views

Need to get more analog inputs Arduino Uno

Im making BattleShip on the Arduino: 2 x grid ((10x10 push buttons) + (10x10 led 5mm)) 2 x grid ((10x10 reed switches) + (10x10 led 5mm)) I made a 10x10 grid of push buttons by setting 10 buttons ...
  • 11
0 votes
1 answer
750 views

Will MCP23017-E/SP be compatible with an ATtiny85? ATmega328P?

I mainly want to also be able to use the same I/O expanders with ATTiny85 projects since those chips have limited pins. I will be doing the main prototyping on an ...
user avatar
0 votes
1 answer
186 views

SX1509 Analog to Digital Converter?

I purchased this product: https://www.sparkfun.com/products/11502 I've wired it up to 5 membrane pressure sensors which provide variable resistance depending on the pressure exerted. However I'm not ...
3 votes
1 answer
851 views

How to read SAA1064 7-segment values

I have a central heating system that displays it's info and error codes on 4 7-segment displays. These displays are driven by a SAA1064, like so: This SAA1064 (datasheet here) receives it's ...
  • 299
1 vote
0 answers
300 views

MCP23017s and arduino problems

I'm not native English speaker, so forgive me my bads. Ok. Here's the deal. In my Arduino UNO I need more outputs and inputs. I bought 3 MCP23017s. One of them for receive states from 8 ...
3 votes
3 answers
1k views

Do you always need a GPIO expansion chip when using i2c?

SUMMARY: I'm trying to learn the basics of understanding how to wire up a simple circuit using the i2c. I'm wanting to build just a simple project involving an LED and a push button with my raspberry ...
  • 1,039
0 votes
1 answer
485 views

MCP23017 in series

I have a hand full of MCP23017 (16 bit multiplexers/ I/O Expander) but I can only get 8 IC on the bus due to the limit of address but I need 200 pins (about 13 ICs) for a 8*8*8 RGB cube and was ...
3 votes
3 answers
481 views

Increase GPIO outputs

I'm working on a project in which I need 32 outputs from an MCU that only has 8 free outputs. To accomplish my goal I have the following requirements: I must be able to toggle more than one output ...
  • 1,012
5 votes
1 answer
2k views

i2c over gpio - level shifter

I'm quite new to this. I have just basic background in electronics. So I would appreciate an advice from someone more experienced. I would like to connect an i2c display to my tp-link wr703n (ar9331) ...
  • 145
2 votes
1 answer
2k views

Issue controlling MAX7301 GPIO Expander via SPI using Arduino Uno R3

I'm trying to write a driver to control a MAX7301 GPIO port expander that will be controlled via SPI. I've used SPI before and it's pretty simple, but I've been working on this for a few days and I ...
1 vote
2 answers
2k views

Problem with transmitting data from PIC18F45K20 (C18) to MCP23017

I am currently testing the MCP23017 (slave device) 16 bit I/O Expander using a PIC18F45K20 with the C18 compiler to transmit data to the MCP23017. The address pins (A0, A1 and A2) of the MCP23017 are ...
  • 61
1 vote
2 answers
151 views

A 4.8v reading on a loose pin 0?

I have a setup that demands that I use all my I/O's on my Arduino Uno R3 board - including the serial pins 0 and 1. So I've initialized those pins as inputs, but when I make a reading on pin 0 it ...
  • 73
1 vote
1 answer
811 views

How do I connect non-I2C devices to an I2C bus?

I'm quite new to electronics and just trying to do my first Raspberry Pi based system: one diode, one pressure sensor and LCD 1602 with keypad shield (the one for an Arduino board). The way I'd like ...