Search found 8 matches

by iot_guy
Tue Feb 20, 2018 9:54 am
Forum: General Discussion
Topic: low voltage on output pins
Replies: 8
Views: 6038

Re: low voltage on output pins

When using a transistor as a saturated switch like this the base current is just (Vmcu_pin - Vbe) / Rbase You just need t ensure that this current is much greater than the collector current divided by the hfe of the transistor. A good rule of thumb is to make the base current greater than 1/10 or 1/...
by iot_guy
Sat Feb 17, 2018 3:02 pm
Forum: General Discussion
Topic: Random String generation
Replies: 3
Views: 2903

Re: Random String generation

Use a random number as the ASCII code for each character in the string. E.g. (not tested) // Generate random string in "str" of length "len" chars static void get_random_string(char *str, unsigned int len) { unsigned int i; // reseed the random number generator srand(time(NULL)); for (i = 0; i < len...
by iot_guy
Fri Feb 16, 2018 11:28 am
Forum: General Discussion
Topic: low voltage on output pins
Replies: 8
Views: 6038

Re: low voltage on output pins

I'm assuming the transistor emitter is connected to ground here. If "the current at the collector is very low" then use a bigger base resistor than 2k (e.g 10k or higher) and see if this makes a difference to the MCU pin voltage. If pin still low do the same test with nothing connected to the MCU pi...
by iot_guy
Tue Feb 13, 2018 11:09 pm
Forum: General Discussion
Topic: Mosfet choice
Replies: 11
Views: 11053

Re: MOSFET CHOICE

Unless your MCU pin is 5 volt tolerant you can't use it directly to switch a P channel MOSFET as for the NMOSFET to be off the gate needs to be pulled up to the battery voltage. Hence the use of a NPN transistor in the diagram (could also have been a N channel MOSFET).
by iot_guy
Wed Oct 25, 2017 9:48 pm
Forum: General Discussion
Topic: Battery voltage reading via ADC
Replies: 7
Views: 14835

Re: Battery voltage reading via ADC

Hi ayavilevich, By "switching the divider", do you mean using a transistor of some kind or is there a better way? Yes, or better than a transistor in this case use a MOSFET. A transistor will have a VCE saturation voltage where as the MOSFET will act more like a switch with just a small resistance (...
by iot_guy
Tue Oct 24, 2017 11:58 am
Forum: General Discussion
Topic: Battery voltage reading via ADC
Replies: 7
Views: 14835

Re: Battery voltage reading via ADC

Hi ayavilevich, I afraid can't find data for the ADC input impedance unfortunately. The original problem posted is probably much more to do with ADC calibration (that WiFive links to) than ADC input impedance. In your case the ADC input impedance will be in parallel with your 20k resistor. But the A...
by iot_guy
Sat Sep 30, 2017 12:57 am
Forum: ESP-IDF
Topic: ESP-IDF failure with both make and make menuconfig
Replies: 6
Views: 7095

Re: ESP-IDF failure with both make and make menuconfig

I have this problem also and none of the steps above work for me. Trev@Trev-PC MSYS /c/esp/hello_world $ make menuconfig make[1]: Entering directory '/c/esp/esp-idf/tools/kconfig' make[1]: *** No rule to make target '/usr/include/sys/_locale.h', needed by 'mconf.o'. Stop. make[1]: Leaving directory ...
by iot_guy
Tue Sep 05, 2017 2:27 pm
Forum: General Discussion
Topic: Battery voltage reading via ADC
Replies: 7
Views: 14835

Re: Battery voltage reading via ADC

What value resistors are you using in the potential divider? How are you calculating the voltage values from the ADC binary value? One of the things to consider is that the divider will add series impedance which will act with the ADC input impedance to form another divider. This is why buffers are ...

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