ESP8266 Community Forum

- Thu Nov 05, 2015 9:53 am #33127

but lethe you talked about "switching" the direction via circuit so LOW = LED on and HIGH = LED off

If you connect an LED to GPIO0 the normal way, anode on GPIO0 and cathode to GND via resistor, the ESP will always be in programming mode and will never go into running mode since this LED will act as a PullDown. So, to be able to connect LED to GPIO0, you need to reverse connections, cathode on the GPIO0 and anode to VCC via resistor. But this means, as lethe said, that the software which control the LED need to be reverse too : LOW=ON and HIGH=OFF.

- Thu Nov 05, 2015 10:07 am #33131

but lethe you talked about "switching" the direction via circuit so LOW = LED on and HIGH = LED off

If you connect an LED to GPIO0 the normal way, anode on GPIO0 and cathode to GND via resistor, the ESP will always be in programming mode and will never go into running mode since this LED will act as a PullDown. So, to be able to connect LED to GPIO0, you need to reverse connections, cathode on the GPIO0 and anode to VCC via resistor. But this means, as lethe said, that the software which control the LED need to be reverse too : LOW=ON and HIGH=OFF.

ah Ha! Makes sense.

By the way, Martin, does it pain you after all of our discussion about the mcp23017 to hear me talking about this stuff? I wonder every day if I should just say "forget it" and use the mcp23017... but my (original) thought was that if I could cut that piece out then it would simplify my entire circuit, and it would be one less thing to buy. But, now I'm not so certain.

Out of curiosity, in my situation would you go with the "simple" solution of just using all of the pins (including pin 0!) of the esp-12e, or would you recommend I go with the mcp23017? I know it's a bit late in the game perhaps to be talking like that, but I feel like I've got a SIGNIFICANTLY better "feel" for things than when I made my first post about the general feasibility of using the esp8266 for the project in general. I've "solved" most of the problems (with so much help from you and lethe, and many others!), but now I keep going back and forth in my head between using the mcp23017 or not.

In ways it's "simpler" to use the mcp23017 actually because then I can just do "normal" output stuff once I get everything in place. In other words I can use the GPIO on the mcp23017 easily for output for the LEDs, and still use a few pins on the esp-12e for my capacitive touch, and of course leaving the GPIO0 pin open for easy programming.

I'd just be curious about everybody's opinions on the matter!

- Thu Nov 05, 2015 11:44 am #33143 Hi, you could always use a 74HC595 shift register to take care of the leds. Only needs 3 GPIOs and the cost is minimal.

- Thu Nov 05, 2015 4:11 pm #33182 Personally, I would use an GPIO Expander. If PCB space is an issue from using MCP23017 28 pins, then I would choose PCF8574 smaller expander which still allows both IN/OUT on the same chip with 16 pins package, cost around $3 for 10 on eBay. (I don't like the 74HC595 since it is output only, and needs 3 wires instead of 2)