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Forum Index : Microcontroller and PC projects : Micromite: connect several digital out pins together for more current?
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| Vampire05 Regular Member  Joined: 06/12/2020 Location: GermanyPosts: 88 |
Hi all, is it possible to connect several digital out pins together on the Micromite in order to be able to draw more current? I have a HC-12 module here that runs in FU2 mode and consumes 16mA when transmitting. The Micromite can only supply 10mA per pin. Instead of putting the HC-12 module into sleep mode, I would rather control VCC from the HC-12 module via DOUT pins on the Micromite. Is that possible? Best regards Artem Edited 2023-05-12 05:52 by Vampire05 |
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| cosmic frog Senior Member  Joined: 09/02/2012 Location: United KingdomPosts: 284 |
You could use a relay or better still a transistor. Here is a video on how to use a transistor as a switch to power your hc-12. |
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atmega8 Guru  Joined: 19/11/2013 Location: GermanyPosts: 722 |
Use a transistor or a logic level mosfet. |
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| Vampire05 Regular Member Joined: 06/12/2020 Location: GermanyPosts: 88 |
I forgot to mention that I have to save every mA because I operate the Micromite with 1MHz from a LiPo (without DC-DC converter) and solar cell. So relay does not work. Transistor or Mosfet would be plan B. Would it work without a transistor? |
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| Vampire05 Regular Member Joined: 06/12/2020 Location: GermanyPosts: 88 |
 Absolute max rating per pin is 15mA and for all ports 200mA.... I think i will give it a try. Is it possible to switch several pins to output high at the same time? Edited 2023-05-12 06:44 by Vampire05 |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6800 |
Please, don't do it. It can so easily end in tears. A MOSFET is the way to go if you absolutely have to switch VCC. The Micromite pins can't reach 3V2 with any amount of load on them anyway. The very best way is to put the HC-12 into sleep mode, but it will draw a tiny bit of current (22uA). If you must switch VCC consider a P-channel mosfet with a 100k turn-off resistor from gate to source. Pull the gate down through a 10k resistor to switch on. The mosfet will have a far lower voltage drop than the output pins of the Micromite. Resistor values are guess and will probably vary with your mosfet. Battery goes to source & turn off resistor. Load is from drain to ground. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Vampire05 Regular Member Joined: 06/12/2020 Location: GermanyPosts: 88 |
You are absolutely right Mick, I can see that mosfet is the sensible solution. Sometimes I tend to go for experimental solutions  For a moment I thought that theoretically you could connect two dout pins and switch them one after the other if the second one is protected by a Schottky diode...  |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6800 |
You *can* parallel outputs, don't get me wrong, but you may have to write a port driver for the Micromite to make sure that all paralleled pins switch at the same time. You will need more than 2 pins though as each pin will have it's own volt drop from its own little mosfet so you need a few to reduce that. A single mosfet is far easier and will have a lower volt drop than several pins in parallel. By the way, to turn the mosfet off change the pin into an input rather than setting it high. You will save about 1uA :) The PicoMite PORT command does switch all pins at the same time, but I don't know about the Micromite. Put a big enough capacitor for the HC-12. They can draw a lot more than 16mA when first switched into transmit mode. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| oh3gdo Regular Member Joined: 18/11/2021 Location: FinlandPosts: 47 |
Vampire05 I had a similar problem with my servo device. It has a PIC CPU and a servo. I tried to turn power switch on with USB power, but it was only 0.5A capacity and servo doesn't work. I tried to add normal capacitors up to 2000uF. Doesn't helped. Then I ordered a super capacitor 0.3F 5.5V from Alibaba. This helped me. There are lot of super capacitors for example https://www.alibaba.com/product-detail/new-and-original-ultracapacitor-super-farad_1600831512894.html?spm=a2700.galleryofferlist.normal_offer.3.5c567786Vg1Q6d ___________ Pekka |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6800 |
If you put a supercap in and switch it via a mosfet then you must fit a surge limiting resistor to keep the charging current below the maximum rating of the mosfet. It's like switching into a dead short. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| oh3gdo Regular Member Joined: 18/11/2021 Location: FinlandPosts: 47 |
Mixtel90 No, I just put a super capacitor and tested it. I works. The PC limits USB current to 0.5A. I used my old PCB and removed old power supply and replaced it with USB cable. When the PC is sleeping, my PIC clock was looking the time with USB power and when the time starts at morning, my PC starts with servo. It pushed the on/off switch. When we went to sleep. it pushed again the same switch. Later I found a similar function in the PC, but it doesn't put PC off. I found the same thing, which worked with HP PCs, but not with my HP550. It is very slow PC, but suits for me. It sends the results to my Internet place and I can follow data at works.  It is used to log with my data logger.  ____ Pekka |
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Quazee137 Guru Joined: 07/08/2016 Location: United StatesPosts: 572 |
I have been using the AP2112K-3.3TRG1 enable pin to turn on/off a group of relays they have their own power feed. AP2112.pdf Quazee137 |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3150 |
That looks like a good find. I've ordered some. PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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