HiLetgo 2pcs PCF8574 PCF8574T IO Expansion Board I/O Expander I2C Evaluation Develop Module

GPIO pins are generally in short supply on most microcontrollers. These boards are a great way to add a couple 8-bit I/O ports to your device. Mine had a base address of 0x20, apparently some have a base address of 0x38. If in doubt code for an I2C scanner can be easily found. You could also just try 0x20 and if that doesn't work then try 0x38.These devices are easily cascadeable, one device can plug into a second (or third, or fourth...) up to a limit of eight. Of course you will have to set the address jumpers provided so each board has a unique address; if your board's base address is 0x20 you can use the jumpers to set it to 0x21, 0x22, ...0x27.One thing I did discover is that you'd be wise to add your own pullup resistors on SDA and SCL; a 4.7k resistor works well.An excellent value for the price.

Using a single GPIO pin on an esp8266 is not a limitation if a unidirectional port expander can be tolerated. I used this part to operate a 8 relay board. In this case I used an esp8266 d1mini. Here is a working YAML sketch:-------------------------------------------------------------------------------------------------------------esphome:name: esp8266-8-relayfriendly_name: Esp8266_8_relayesp8266:board: d1_miniframework:version: recommended# Enable logginglogger:level: debuglogs:mqtt.component: DEBUGmqtt.client: ERROR# Enable Home Assistant API#api:#encryption:#key: "q0wRAARhTmThOjrv6MpTmtEduXIIxZ9XNB5RCcWykdY="ota:password: "a141235ccb9cb645e296e911ecfb09b7"wifi:ssid: !secret wifi_ssidpassword: !secret wifi_passwordmqtt:broker: 192.168.11.238username: !secret mqtt_usernamepassword: !secret mqtt_passwordcaptive_portal:i2c:sda: D1scl: D2scan: trueid: bus_afrequency: 50pcf8574:id: pcf_expanderaddress: 0x20pcf8575: falseswitch:- platform: gpioname: "Relay 1"id: relay_01pin:pcf8574: pcf_expandernumber: 0#If the relay starts NC, add inverted: trueinverted: true- platform: gpioname: "Relay 2"id: relay_02pin:pcf8574: pcf_expandernumber: 1inverted: true- platform: gpioname: "Relay 3"id: relay_03pin:pcf8574: pcf_expandernumber: 2inverted: true- platform: gpioname: "Relay 4"id: relay_04pin:pcf8574: pcf_expandernumber: 3inverted: true- platform: gpioname: "Relay 5"id: relay_5pin:pcf8574: pcf_expandernumber: 4inverted: true- platform: gpioname: "Relay 6"id: relay_6pin:pcf8574: pcf_expandernumber: 5inverted: true- platform: gpioname: "Relay 7"id: relay_7pin:pcf8574: pcf_expandernumber: 6inverted: true- platform: gpioname: "Relay 8"id: relay_8pin:pcf8574: pcf_expandernumber: 7inverted: true________________________________________________________________________________Remember to use the optically isolated function of the relay board for maximum safety.

If you need to expand the number of I/O pins on your Arduino/ESP MCU, look no further than here.This modules gives you 8 digital pins without using any other pins than your I2C bus and power. I am working on connecting mine to a 8-relay module. Since I am working with high voltage, I didn't post any pictures yet. :)Pro Tip: As others have said, the I2C address may be 0x38 or 0x20. If you have an I2C Scanner sketch (and you should), it takes a minute to figure it out. Don't fret. Change is part of life.

Got this port expander for interfacing Arduino with 4x4 matrix keypad. It does the job well to save I/O pins on arduino projects.

This device will not work with any address other than 0x20, even if I only have a single device connected. Whenever the address is changed it causes my Arduino to slowly power down.

Update : The seller reached out to make this right, and were very apologetic for the original issue, so I've updated my review from 2 stars to 4 stars, due to the good customer service.Ordered this pack of two, but one of them arrived without the right-angle header on the board. It wasn't damaged or broken in any way, it was entirely missing ! They just hadn't soldered on the connector during manufacture, and put it in the packet without the connector installed.The chips on the board were Philips A series (0x38 base address). Note that you will need a pull-up resistor to drive anything much with this chip (even driving a Relay via an Opto, I needed to use an external pull-up. I used a 3.3K pullup when using 3.3v I/O, which seemed to work fine)

The Address pins (A0, A1, and A2) on BOTH the boards I received were grounded on the PCB.The pin outs on the jumpers when holding i/o pins on the top, where VCC, and the next 2 columns were shorted on the PCB between Ground and AO, Ground and A1, and Ground and A2. This prevents you from being able to Unground a pin to pull it high. It also means when you try to pull any Address pin high you short out the VCC to Ground. In order to change the address you must un-solder the Address pins you want pulled high from the PCB.

These boards have their address pins hard tied to ground in the address selector switch circuit. If you try to select anything other than ground for the address pins it will short your supply to ground. fortunately the trace that does this is available on the backside, and if you cut with an exacto knife as in the picture full functionality will be restored with 30 seconds worth of work. Note: only cut between the jumper pins as shown, I scratched a bit higher but did not cut those traces.I design chips much more complex than these, and regularly do board mods like this, but I could see less skilled users having a serious problem with this if they needed more than one address.I noticed this product now shows a red board with dip switches instead of the blue board with jumpers, it's fairly likely the red board works properly. I like how the blue boards are chainable though.