Search found 38 matches

by bobtidey
Wed Jul 22, 2020 9:23 pm
Forum: ESP32 Arduino
Topic: Many ESP32 modules on single wifi access point?
Replies: 3
Views: 648

Re: Many ESP32 modules on single wifi access point?

I don't think it is specifically to do with esp32, rather a question of the size of the packets and the rate at which they are being sent. If the interval between each mqtt packet is a decent amount then there should not be a problem in supporting a large number of devices. I have about 35 esp8266 s...
by bobtidey
Wed Jul 22, 2020 9:11 pm
Forum: Hardware
Topic: Pick up WiFi noise
Replies: 3
Views: 857

Re: Pick up WiFi noise

White noise at 80 MHz is a meaningless requirement. White noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. (Wikipedia) So if it was white then the power density would be the same at 1MHz,10MHz,100MHz etc. If you give some backgrou...
by bobtidey
Tue Jul 07, 2020 8:08 pm
Forum: ESP32 Arduino
Topic: How does ESP32 drives OLED 1106
Replies: 5
Views: 673

Re: How does ESP32 drives OLED 1106

These display modules can either be SPI or I2C. It sounds like yours defaults to I2C. I2C connects to the SCK & SDA pins. They should normally have the required I@C pull ups on the display board. DC in I2C is used as an I2C address selector. If it is pulled low then the address should normally be 0x...
by bobtidey
Sat Jun 06, 2020 11:44 am
Forum: Hardware
Topic: ESP32 powering a solenoid
Replies: 12
Views: 1769

Re: ESP32 powering a solenoid

I think that even for the 2n2222A version it is hard to come up with a worst case design that provides sufficient Ib to saturate and yet doesn't potentially try to draw more than 40mA from a GPIO. 2n2222A max Vbe Sat @ 500mA Ic 2V might be a bit less at 300mA but not actually specified Assume GPIO V...
by bobtidey
Fri Jun 05, 2020 8:43 pm
Forum: Hardware
Topic: ESP32 powering a solenoid
Replies: 12
Views: 1769

Re: ESP32 powering a solenoid

Just to amplify further why I think trying to exploit potential 40mA capability of a GPIO would be a bad idea. 1 Vbe sat of a 2n2222A could be 2.0V 2 Vo of a GPIO at 40mA could drop to 2.6V 3 So to guarantee 30mA Ib what base resistor would you use? 4. Then under typical conditions where GPIO might ...
by bobtidey
Fri Jun 05, 2020 8:27 pm
Forum: Hardware
Topic: ESP32 powering a solenoid
Replies: 12
Views: 1769

Re: ESP32 powering a solenoid

When using bipolar transistors for switching you do not use the current gain (beta) to determine appropriate base current. That parameter is specified when the transistor is in its linear region with a significant Vce. Gain drops off dramatically as Vce falls. The normal 'rule' for switching is that...
by bobtidey
Thu Jun 04, 2020 8:53 pm
Forum: Hardware
Topic: ESP32 powering a solenoid
Replies: 12
Views: 1769

Re: ESP32 powering a solenoid

Using a bipolar transistor like a 2n2222 is not a great idea for switching the current to the solenoid. For a 300mA solenoid you would need to feed about 30mA into the base of the transistor to saturate it (switch it hard on). That is to much for a GPIO pin. You could use a darlington transistor lik...
by bobtidey
Sat May 09, 2020 8:52 pm
Forum: Hardware
Topic: GPIO drive strength.
Replies: 6
Views: 3110

Re: GPIO drive strength.

As has been pointed out a series gate resistor does very little when using a MOSFET driver. The only possible benefit would be to add a degree of protection to the GPIO pin if there was some catastrophic failure in the MOSFET device. These tend to be very reliable devices and I do not add a series r...
by bobtidey
Tue Feb 25, 2020 11:21 am
Forum: ESP32 Arduino
Topic: ESP32-CAM Problem with not enough pins
Replies: 9
Views: 5500

Re: ESP32-CAM Problem with not enough pins

You can use the TXD and RXD pins as GPIO.

Obviously they are not operational during a flash upload operation which may mean swapping wires to do uploads but if you use OTA then that doesn't matter after the first flash.

Using RXD doesn't affect any serial debug print but using TXD will.
by bobtidey
Mon Feb 17, 2020 8:56 am
Forum: ESP32 Arduino
Topic: SAMPLING AUDIO - How to handle large data?
Replies: 6
Views: 2397

Re: SAMPLING AUDIO - How to handle large data?

If you use an esp32 module with 4MByte PSRAM (e.g. WROVER) then you can store your whole capture in a buffer before writing out to file.

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