I just got cheap stuff such as an 858D hot air station. Any Chinese clone will do and a TS100 soldering iron. Nowadays the Pinecil would be a better choice.

Thanks again for the advice. I made a working prototype and attached it to my pump. The PCB is also made at home which is something I’m trying to learn.

For now I’ve used just optocouplers to drive the mosfets, since pulling p-type gates down to above -24V seemed like a hassle. I’ve ordered some IR2210 gate drivers and intend to use those with PWM later to not have to use a buck converter.

Here’s a video of the pump. https://drive.google.com/file/d/1qKDBLTbYi2Fbu3UOXpxqSoj00oueWK-K/view?usp=sharing

And the pump in action. https://drive.google.com/file/d/1--HyeJGtYS5dgsjgelE6CrOm2vbBmwXU/view?usp=sharing This version has a stepper motor instead of a DC motor. Stepper motors have low speed limit which is why I’m trying to change it to DC motors.

Good one. I haven´t considered that. The 7818 will only deliver current for very short bursts but perhaps that already is too much. I’ll look into the PWM solution.

That would require an H bridge with two Pmosfets on the high side indeed. And a way to prevent the gate voltage from going below -20V on those.

The PWM frequency on arduino nano is also a bit slow for controlling a motor so a 555 circuit needs to be added then. I have a large amount of XL4016 modules that work well though.

Thanks for the advice!

Well, the whole setup is a semi automatic greenhouse. It has a 12 channel peristaltic pump, grow lights, heater and a plant shaker for pollination. I’m attempting to grow indoor tomatoes and chili’s. Not weed although I have learned a lot from weed growers.

The system runs on a 24V power supply so that is easily accessible. The 18V comes from an LM7818 and the motor speed will be regulated with a buck converter module.

The off state is with both inputs at 0.

Between 4 and 8V. I’m driving a pump with a 12V rated 775 motor. Running it at full power makes the pump go too fast and with a lot of noise.

It’s kind of an overpowered motor for this project but I have a couple of spare ones.

Proto on Android.

Right, sorry about that. I made the simulation on my phone with the Proto app.

I figured the push pull part is good practice with mosfets. It’s partially the learning experience and if the motor stalls it could draw several amps.

I won’t be doing PWM, just on and off so maybe just the optocoupler is good enough.

I’d have to order dedicated gate drivers and have a lot of 547 and 557 transistors in stock at home.

Haha. I do not want this one to catch fire.

Hmm allright. The power saving isn’t that significant so perhaps I should find a better way for it.

If the house burns down because of that your insurer will likely be difficult about it. You should also check the policy of your insurer, perhaps the cause of the fire is irrelevant.

As for fire safety. I always put my electronics in non flammable environments and make sure that everything is fused with either a current or thermal fuse.

Anything with high current consumption goes inside a metal box so that even if it does catch fire it can’t take anything with it. 3D printed enclosures are fine if you mount those inside a metal bucket for example.

Thanks. Haha no I fully intend to grow vegetables. I don’t even like weed. The last time I smoked it eas 20 years ago, it gave me a panic attack and I never touched it since.

For my use case fidelity is no problem at all. My spot size is minimally about 0.1mm and I’ve increased it to 0.5mm to increase speed.

For photosensitive dry film you don’t need much power so you don’t need max focus. In fact you’re likely to burn through the film with the smallest spot size.

Toner transfer has been messy and unpredictable for me. Also alignment with double-sided PCBs is more difficult this way.

That is a good point. I was under the impression that solder mask is mostly for safety and convenience when soldering so it only flows where you want it to.

Creating a mask that works for solder mask as etch resist does require some tweaking with the SVG files. I’ll give it a try for a few small boards to see how well it really works.

Why is that? I understand there is a tiny layer of exposed copper on the side of the traces but copper tends to form a protective layer of oxide.

Tooting my own horn. I have something to add. With the UV “Mechanic” solder mask that gets sold on Chinese webshops pre-heating the solder mask makes a HUGE difference. Apparently it contains some volatile components that interfere with the curing process.

Heating it to about 80-ish C for a few minutes and optionally letting it cool down causes the laser to almost instantly cure the mask. Any non-exposed mask will be easily washed off with some IPA.

Yes that I found as well but have/had trouble understanding why it would be built like this. Also why a MOSFET would be designed internally like this. If you want more power capability you’d get a bigger MOSFET rather than two tiny ones in parallel right?

This page helped me understand the setup. I’ll post it here just for informational purpose. It took me a while to find this. https://electronics.stackexchange.com/questions/203463/dual-mosfet-8205a-lithium-battery-protection-circuit

It’s related to the internal body diode of the N channel mosfet, so two of them are in series but reversed. When one MOSFET is activated, current may flow easily in one direction but be reduced by the body diode of the other. When both are activated, current may flow easily in either direction.

It seems they don’t really prevent discharging or charging separately due to the body diodes but they can cut off the battery alltogether.

That’s good. My switching frequency is a few times per hour.

I am a little bit concerned that the slow rise/fall time make the MOSFET go outside its operating parameters for a fraction of a second. The resistance gradually changes meaning the mosfet will dissipate more power but also less current will flow.

So if you switch many times per second the gate capacitance with the resistor acts as a low pass filter reducing the gate voltage.

Replying to myself for informational reason. Modifying voltage was more or less successful. Both optocouplers transmit a reference voltage, so both need to be adjusted simultaneously.

This can be done by changing the value of R19, a 23.2k smd resistor close to the output terminals.

I’ve attached a 10k pot with a 10k and 6.8k resistor in series and successfully modified the voltage down to 22.5.

The power supply itself is a piece of crap though. It claims to handle 400W but anything over 150W causes the short circuit protection to activate, never mind overheating at 150W very quickly.