I haven't done anything like this in years and never had all the theory anyway. The circuit below is for an intervalomer using a ProMini which has been lying around for a long time, and with an ESP-01 operating in setup only. It was "designed" from scraps of information with parts from Jaycar over the hill.
The perf board for the whole thing is getting seriously crowded, but I am wondering about putting in a 100uF as well. There is just enough room for that.
The circuit looks like okey. Is it working in its application?
Do You mean to upgrade both 10 uF to 100 uF? It can't be wrong but what about adding some 100 nF ceramik, to kill eventual spikes, as well?
Better to use the EN pin of the ESP-01 to switch the ESP on/off (HIGH is 'on', LOW is 'off').
Note that you also need a 2k:1k divider there.
Leo..
Thanks for your comment.... No, I was wondering about adding a 100uF to the 10uFs already there, and indeed I thought about a 200nf that I have lying around. I suppose it might be better to replace one 10uF with a 100uF. Nothing has been actually made yet and I am just seeing if I can squeeze it all onto a 24x30 perf board.
Well, there you go, I have never had an ESP-01 and had no idea about the EN pin, I now guess you are alluding to pin 4, as shown. I will check Pieter's ESP Page.
Thank you
Never used one too, but I do use bare ESP-12 modules, which also have that EN pin.
Leo..
I believe both RX and EN "idle" high. If that's true, then the resistor dividers might sink a couple milliamps most of the time. If either pin is pulled high internally, then a series diode might be a better choice. The Pro Mini could bring either line low, but not high. And even if you had to add an external pullup resistor to 3.3V on those pins, along with the diode in series, it still might be a good solution. Well, if the radio is going to be off most of the time, then the divider would be fine for EN. Not sure about RX.
If you were starting from scratch, I think you would run the Pro Mini at 3.3V, 8MHz, eliminate the boost converter, and get a better 3.3V LDO with a much lower dropout voltage. Maybe even run it all on a 3.0V LDO if the ESP would deal with that ok.
Suggest you use two converters.
BTW, You might want to look at removing the potentiometer.
Boost/buck converters come in small form factors.
3.3V Step Down/Up
Well, I'm glad I asked before I got too deeply into this...
I should have been more forthcoming: This project is an intervalometer with clock for use in astrophotography - specifically, ISS transits. A lot of the stuff, 5v ProMini, LEDs, 7221s are already lying around but I haven't really done any of this power supply stuff since about the invasion of South Georgia so I guess there are slicker ways of doing this and certainly wondered if I really need an adjustable pot. Further, I guess I can expect more modern modules to have the requisite caps on board.
I'm not sure what this involves. The radio is off virtually all the time. It is just there to ensure the DS3231 is truly up to scratch. The only alternative to the usual 1k/2k divider I know of is with a BS170 MOSFET
but I have never used it. It didn't occur to me to use it now, but this might be the time, even if only for ESPs Rx.
OK, I found one which looks like yours and specifically for ESP8266 even though it is coy about the current.
And another to deliver up to 480mA @ 5v.
Both to be in parallel on the 18650, rather than the up/down daisy chain I had before.
Even though I think I only have one to hand, I am tempted to use two NMOS, just for the elegance and perhaps greater efficiency. Not that that is so important. The ESP will only run for a few seconds, the display a few minutes, and the whole thing for no more than a day.
Confused..
Why a DS3231. The ESP-01 has a crystal clock.
Do you need "time" or "local time".
The ESP-01 can do that when booting near a router.
Why WiFi anyway.
What is "everything else". Can't it run off 3.3volt.
Then you could use a LiFePo4 battery, so you don't need an LDO.
Why the ProMini. You already have a processor.
Leo..
The mosfet circuit gives you bidirectional level shifting. But both EN and RX are unidirectional. So you only need pullup resistors to 3.3V on the ESP pins, and diodes pointing back to the Pro Mini pins. The Pro Mini can take those lines low, but when it takes the lines high, that's blocked by the diode.
As I said, the WiFi is just to ensure the RTC is up to scratch on startup, this is done just before leaving home. From threads around here, I understand ESP8266 does not have a crystal and the on-board clock leaves a lot to be desired. I guess this is OK when regular update from NTP is available, but not in the field, .
The "everything else" is six 2x7 led displays 0.8", colon LEDs, two 7221s, a 4x3 keypad and I guess two or three extra buttons I have yet to really think about. I already have most of this stuff, along with a DS3231 with square wave output, and a 5v ProMini that has waited a long time for employment.
I understand 7221s are very particular about getting 5v. Also, ESP8266 i/o pins are only good for 12mA.
Local Time is used
Every ESP8266 I know has a true crystal clock.
That makes it as accurate as a poor quality untrimmed uncompensated RTC.
Not sure how much it will loose/gain in a day. I guess it could be a few seconds.
Leo..
OK then, not for the exact reasons I understood, but leaves a lot to be desired all the same. This job will suffer environmental variations that would frighten a DS1307 and it is pretty clear a DS3231 is the way to go. The whole objective is peace of mind in the heat of the moment on a cold clear night - something my commercial intervalometer doesn't deliver.
I'm afraid I'm not sure what you are saying here. I understand about MOSFET being bidrectional, unnecessarily, but not about the diodes. I think I will go back to dividers, they being common practice after all, and I can probably afford the current. Besides, I can't find the MOSFET.
The schematic below shows the modifications needed to operate an SD card (3.3V) from a 5V Arduino using the SPI lines. The module doesn't have any voltage translation, but does have pullup resistors to 3.3V on the SD card pins. The modification just inserts a diode into the output lines of the Arduino. When the Arduino pulls MOSI low, the SD card pin drops to about 0.6V, which the card recognizes as low. But when the Arduino takes MOSI high to 5V, the diode blocks any current from getting to the SD card. Instead, the pullup resistor brings the pin high to 3.3V. So the card is protected from the 5V signal.
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