A very welcome example of the realities of engineering design. I was reminded, somewhat, of my time as a chemical engineer student. We spent an inordinate time learning to calculate the required size of a heat exchanger for various situations. Thermodynamics entail calculations that are not so much difficult as they are tedious but we were required to come up with results of very fine tolerance. After graduation, we were all to discover that said heat exchangers were not bespoke items but were, in fact, "off the peg" components. Most of the time we would be require to select from, maybe, four or less items way bigger bigger than our precise calculations demanded. Further experience taught us that, unless one was designing a formula one racing car, ones life was filled with Hobson's choices. This video was valuable for sharing such compromises that are the basis of all design. All too often, maker videos skip this stage of design, leaving the viewer with the impression that the choices of components spread out on the camera table were the obvious choices and if you couldn't see that, maybe you should leave the designing to your betters.

Another popular box is called a "hammond box". They are made of aluminum and other various materials. They are also very affordable and easily cut or drilled. I did a project last fall similar to this one. It kicked a heat lamp on when the temp got too low for my kids rabbits. I love these projects but never have time in the warm months BUT! winter time is coming. Great video! :)

great video, i was actually thinking of designing a pcb so the timing od this upload was on point!

Sir, I love your videos. The way you explain the topics, the tone of voice, everything is perfect. Thank you from Canada.

Very good project, I know you do not want to change your project, which is looking very good indeed, but one thing I would do is to move the relay and put it sideways to the transformer, so tha the low voltage coil stays on the low voltage side. I get very nervous when I see low voltage tracks running in the same side as mains. You know arcs are unpredictable. I would also move the slots underneath the transgormer and relay to avoid any arcs making visits to the low voltage side. I made a soft start for amplifier I am doing and run into the same issue of mains in the same PCB (and in Brazil we have 110V only). My contribution to the excellent work you do.

Toolstation and CEF sell PVC back boxes and blanking plates, which will drill fine. They also have a knockout at the top (or bottom) for 20mm conduit, but you could put a gland there instead.

Hi Ralph. Really nice to see someone going through the overall mechanical design process as I find it immensely frustrating that videos appear of neat tools/circuits but zero consideration of how they'll be fitted/mounted/used in anger! Good job ... More please. Some points for you to consider for any future majns control projects. 1. Complete isolation of control electronics from mains level can easily be achieved by using an opto-coupler like a PC817. These (or similar) are ubiquitous in computer ATX supplies ... One reason to NEVER bin them but scavenge out ALL the parts ... mechanical, electrical AND electronic. Others have proposed moving the relay to have the low volts on the low volt side BUT most relays will have the common pin (high or mains power) sitting in between the coil supply pins ... NOT the best scenario! Using an opto-coupler completely removes this problem. Coil power can be derived simply from the mains side by a simple resistive or capacitive dropped with some suitable filtering caps. The input side is fully Arduino) ESP compatible requiring only a simple series resistor from the output of the MCU to provide the right drive current for the input side. It also means that no tricky slot cutting around the common pin is required and separation on the opto is significantly greater anyway. 2. Many people also don't realise that there are dedicated triac opto drivers that INCLUDE zero switching technology so BUYING a commercial "electronic relay" is generally completely unnecessary since the triac is either on or off and does BOTH at the zero point when required (for YOUR type of design) Again, it's FULLY isolated to >1 or 2 kv or more, minimal external components, as small in total footprint as a small relay, minimal heatsinking required (it's either fully on or fully off for your requirement) and 100% directly compatible with MCU output levels. Switching up to 13A for a wall heater can use a low cost T2035H-6I 20A, 600v, 1v trigger, 5(£1.28 - 1 off from CPC/Farnell). PLENTY of practical design ideas online for the MOC20xx series optos ... Worth taking a look at. 3. When cutting out PVC/ABS front panels by hand, whenever possible, mark up and cut from the inside out as any slight errors or slips can more easily be disguised. 4. Fit displays with bezels to the OUTSIDE of the case wherever and whenever possible and make up a short jumper cable to achieve an even more professional looking finish ... Also hides those slight cockups we all make when hand cutting. 5. When cutting rectangular holes in plastic do NOT use the sharp edge of the blade ... Use the BACK of the blade to 'scrape' through instead. Tape a metal ruler to the panel along the OUTSIDE of the line you are going to cut. Use the edge as a guide and ONLY cut a max of just over halfway from each corner so that you don't cut past them. Do each line in turn ensuring you finish on a long edge for maximum accuracy and control. Hope the above provides some useful input for your viewers as well as yourself. Bonus tip: One final thing which is a pet thing of mine ... Try, wherever possible to use ferrules (bare ones are fine) when connecting wires to screw down terminals, even IF they have the protective internal tabs ... They insert MUCH more easily and are WAY more secure. Crimped is best but for those with limited budgets and/or tools, soldering is fine and still better than bare or soldered wires.

This video is much better that any university!

Hi Ralph, yep lots more to do when you have the software and hardware running on the bench ! I have had PCB designs sitting there for ages and I check them over and over again and I have found problems on my second and third time through so its well worth taking your time at this stage ...measure twice cut once !.....cheers.

Big Clive always seems keen on slots in the pcb to isolate mains traces from low voltage traces. Seems like a good idea to reduce mains voltage/current from tracking through surface dirt and grime from mains area to low voltage area over the years.

lots of good information here, thanks for sharing

Great walkthrough of the problems with making a new design/Project Thanks for sharing your experiences with all of us :-)

I was just pondering this, regarding experience. School can only take you so far. UKposts is invaluable for showing broad theory. Thank you for sharing some insight Ralph

Hi Ralph. Great video. You may want to use noBacklight() to turn off your LCD display instead of having to use a relay to turn off the LED via the jumper. Dimming probably won't make that much of a difference as you probably can't read a dim display from your desk anyway. noBacklight() will turn of the LED completely from inside your sketch. Safe yourself some wire. Thanks for a very informative tutorial. Best wishes, Gord

Well talked through.

You can PWM that pin on the display directly from a GPIO pin, it is only a single LED after all. I know you want to do it right, but that method works perfectly on my 2004 heating controller and climate readout display run by a Tasmotised Wemos D1 mini, to make it a nice but not full brightness throughout the day, and to dim it at sunset so that it doesn't burn my eyeballs out later on. Also check out your local electrical suppliers for enclosures, I use 'Gewiss' boxes, which you can drill or cut to your hearts content, and they are very robust while being suspiciously cheap for something so good.

Hello Ralph, first of all many thanks for the project. It is really great. But I would have a few objections: 1.) Try (as Superdau already described) to separate the 230V AC from the extra-low voltage better. I got a stomach ache that you have 230V on one side of the board and 12V on the other side directly above each other. Better: Place the relay below the transformer and then really all 230V lines on the right hand side. 2.) Supply the DS18B20 sensor with 3.3V. Not with 5V. First: It works (probably not) I tested this some time ago with the ESP8266 and second: The inputs of the ESP32 are (in my opinion) not 5V tolerant. 3.) Check if the P-Chanel MOSFETS are really completely switched off at a gate voltage of 3.3V (at a source voltage of 5V). Better: Use a combination of N- and P-Chanel MOSFETS. 4.) I would turn the ESP32 by 180degrees. Then the USB connector is on the left side and you could connect (with a small hole in the case) a USB cable. 5.) Make sure that the line to the DS18B20 is far away from 230VAC lines. 230VAC are very "dirty" and cause interference on the One-Wire bus when switching. (Unfortunately I had to make this experience) 6.) Check if the traces for the 230V circuit are wide enough. After all, 8A must flow here. These seem a little "thin" to me. I have already made some 230/5V boards. There is already really a lot to consider. But, as I said great project. Keep it up. Best regards Frank

Thanks for sharing

Ahhh, gotta gouge my eyes out after seeing an auto-routed board, especially a simple one like this. Fixing the auto-routing will most likely take as much time as having in done manually in the first place ;) . Putting the *relay besides the PSU brick* should easily possible. Then the mains/low voltage separation would be much more obvious. Not that it is a problem, if you move the tracks a little, there's enough space for separation. But better component placement would get rid of the need to even think about it (and not using the auto-router ;) ). I've never used EasyEDA (was an Eagle user in the pre-autodesk times, now KiCad user), but there should be an option for a keep-out zone/clearance around a *hole* (and not only for copper, but also solder mask for example). I can't imagine something basic like that would be missing from EasyEDA. What pretty much does what you did, but without having to manually draw circles, is to *insert a pad not connected to any net* . Set the pad diameter to the diameter of the screw head/washer plus some wiggle room (and pad drill diameter to screw diameter obviously). You will have a copper pad around the hole, but since it won't be connected to anything it doesn't matter (and your way of drawing the circle has that anyway). The best option would obviously be to not use the auto-router, then you wouldn't have to worry about tracks suddenly being to close to a hole in the first place. Did I mention that auto-routers are pretty bad? ;) The *connection of two of the MOSFETs is weird* . It looks like you are switching the high side of the with an N-channel MOSFET. Same thing with the LCD PWM MOSFET (although I don't see where the "LED" signal is coming from). I'm pretty sure those FETs are on the wrong side. Does the ESP-module have integrated level shifters? I don't see pull ups for the I2C bus. You are also pulling "DQ" to 5V. An *ESP32 is not 5V tolerant* on its pins. Without logic level shifter you are using the ESP's internal ESD protection diodes to clamp the "DQ" pin voltage to 3.3V plus a diode drop through the 4.7k resistor. I don't know, if the internal diodes can handle that continuously (check the data sheet for the maximum clamping diode current).

Very nice video Sir

Thanks for this video. I wonder if you could give some more detail as to how to create the 'boundary rings' that you mention around 20:30 to keep the HV traces away from the mounting holes. I look forward to all of your videos!

When we designed a project at work - in prototype form, we used an OHP transparancy.Print any letters etc you want, and create a window for your display, then mask the display area, and spray the back of the film. You end up with a neatish front cover that hides a multitude of sins!

Nice stuff. If you only need the reset button for emergency cases, you could drill a tiny pin hole through the front plate., right over the switch. Much like the emergency release on DVD players

remember you need to check the creapage and clearance distances between the mains and any low voltages. plastic screws for the display would help keeping the box double insulated, so i would drop the metal clad leds. Avoid bringing any metal that can be touched out of the box. if the live fails to the low voltage these could become live. for the reset fit the switch behing a hole maybe on the side of the box.

Hi Ralph, love watching your videos and your finally doing one around my field. as ever you know what your doing, but if i can throw in a few pointers i would have done differently, which others may have suggested, 152 comments atm was way too many to scroll through lol. firstly the tracks for your mains on the PCB. you mention 8 Amps for the heater, so i would check out the track widths which look way too thin as i see them, also worth checking the technical data for the terminal block you are connecting the mains with, just to be sure it is rated for the application. on another note, when putting mains onto a PCB, i tend to only have them on one layer, usually the bottom layer which helps minimise any risk of contact. and lastly, the importance of protection, i see you have not allowed for a fuse? other than all that at first glance, it looks fab. oh regarding the cut outs on boxes, i sort of cheat as i have a laser cutter. if ever you need any cut outs doing, maybe i could help in the future. Cheers Phil

Great work, good explanation. You could have placed the relay next to the transformer and thereby keep the low voltage on the left side and high voltage on the right side. -Are you soldering the LED's to the board? -that could give you a hard time mounting them, even more when yo need to open the box. Love to see it finished.

Ralph, you asked for it (peer feedback)... Your FETs Q2 and Q3 won't work as intended. They are n-channel FETs and would need a gate voltage higher than 5V to turn them (fully) on. BTW: The 2N7000 may not turn on all the way even on location Q1. At least it will not turn on to a very low resistance. Check the Vgs voltage in the datasheet. The ESP only drives 3.3V signal levels, or did I miss a capability? And since we are at voltage levels. The DS18B20 DQ pin is pulled up to 5V. So please check if that pin is 5V tolerant. I actually use the DS18B20 with a VCC of 3.3V and it works fine. So you can supply it with and pull it up to 3.3V.

yes a lot of our new EE's have weak how-to info, and the O-scpoe is more of a Zero-scope checking things like 480vac, encoders , etc...:/ as usual another great vid...💪 thanks.😁 easyEDA looks interesting, however about a year ago KiCad was what i went with... another fun learning curve...😘 and made footprints, etc. the PCB came nice...:)

Hi Ralph! I'm glad that i some 15 years ago decided to learn how to make 3D drawings. The 3D printers was in their childhood and i knew that i would be able to afford one at some point. And whats the point of having a 3D printer, if you can't express in drawing, what you want to achieve :-) That gives me an enormous freedom to day, when drawing PCB s and enclosures. And further more, - I know where i can send the complain if somethings does not fit. Have fun, and have a nice day Regards Jens

Theres a lot of wifi mains sockets suitable to plug the heater into, so no need to put any electronics into the heater enclosure just plug the heater into the smart socket. For your low power control box you could incorporate a mains socket, sort of inserted into a cutout in the back of the control box enclosure. You could then plug in a wall wart, but maybe instead of a 3 pin power outlet in this mains socket there are usb power outlets designed to fit the pattress box and you could then feeds your low power circuit board with a simple usb lead all inside your enclosure. Your esp32 then sends appropriate wifi commands to your wifi enabled heater socket. Ok, smack my wrist, this is a bit of a redesign suggestion which is probably not appropriate, but it does eliminate any possibility of getting anywhere near mains voltages.

you could move the relay closer to the psu so that the low voltage to the coil does not need to go close to the mains. it the heat and stby leds are on the case you don't need the pcb area taken up by the body shape of the LEDS, just a 3 pin connector.

21:55 don't forget that in many commercial products that they also don't bother to line up LEDs on the circuit board and instead use light pipes. You could do the same with a piece of slightly oversized acrylic rod. Or same sized if it doesn't bother you that the brightness might vary between units that are off by varying amounts.

Excellent video explaining your thought process. Only thing I would have added into the consideration (which you probably did but just didn’t voice) was that it is worth not modifying components like the fire which I might expect to replace when they fail. If I put a lot of effort locating a hiding place for the electronics inside this particular heater is there any guarantee, when I need a replacement, that I can get exactly the same model, or one with a similar hidey-hole? Do I want to repeat the steps to re-embed the controller int9 this new unit? Sounds like work I don’t need. Much better to utilise the interface that most heaters provide ie the lead and keep things simple. Great project and thx for sharing. 😀👍

Thanks for the tip on how to create a slot in a pcb. I’ll have to see if my pcb app supports that.

Awesome video. I like the level of detail. My two cents: For housing and finding the right box: maybe 3d printing is also an option you didn't mentioned. For PCB design: I like KiCAD :) ....

keep your low voltage the same distance away as the relay pins and from the contacts. Cut your slots there. Make your mains power tracks at least twice what you have now or you will burn out the tracks on inrush current. Leave tracks open and fill with solder if you need to. An overloaded track will coil up and short out. Whilst you may have a 15 amp relay, you have two amp PCB tracks. Slots are nice, but when it comes to inspection, they use distance. CE rules are a minimum of 6mm.

I enjoyed your sharing your thinking process on the design and future changes that might happen. VERY INFORMATIVE. Thanks. P.S. One question. Why didn’t you orient the relay and the transformer next to each other so that one end of the PCB was mains and the other side of the PCB low voltage with a gap in the board between them? Was it a limitation of the size of the box?

printing the 3d view on a 3d printer would be nice for some projects, to test fit inside a case or with other boards. 11:30 calipers can also be used for depth, using the "tail"

Hello Ralph, I found both the schematic symbol and foot print for the Myrra 47246 on Farnell via Ultra Librarian which is always a good source.

You use the long pointy thing at the end of your caliper to measure things in deep holes :)

I have cut 16x2 lcd's into a case lid the same as yours, quite neatly by marking out with an ink type marker pen (fine tip) and then cutting, ever-so-carefully and a bit at a time using a steel rule to begin with as a guide and a stanley knife. Start in one corner then cut about half way along, reverse and cut from other direction. Have to be really careful though as any slip with a finger in line will be disaster. Still, your box is a couple of metres away so who will know. :)

Hi Ralph great video just one thing, the track size on the pcb look a little on the small size for carrying the current of the heater?

SSR can be mounted on any thermally conductive surface of sufficient area. I've used steel enclosure side panels. Read the device datasheet for guidance.

I don't remember if you are into 3d printing yet, but if you were, you could easily print a black bezel to snap over the cutout for the led just to dress it up. Purely cosmetic. Ether that or invite Clickspring over with his micro-files to clean up the edges for you!

yer you made a nice lay out there that half the battle lol.. trying to make all the holes and slot alright is a night mare, sometime using masking tape on the front plastic helps to make markers and helps drill slippage (of which im a pro at lol). nice video again sir, i do like your content. please keep up the good work :)... it must be a night mare comming up with videos i guess theres only so many things we can make lol.. see you soon fella :)

Hi Ralph. I'm curious about your choice of the fuse. I saw in another comment you are using a 1Amp glass fuse. I was wondering in what circumstances would you have selected a ceramic version? Also with it feeding a transformer will you be using a T (time-lag) or an F (fast blow)?

I have to learn not to send off a pcb until a few days after my layout is done. About the time the fab house does the solder mask I think of something I missed 🤔🤭😕

In the spirit of community feedback, I see a trace coming from the RST pin going to the keep out zone for the antenna. But it looks like it is not going anywhere :)

When I was doing work experience in school, I went to an electronics factory. I was in the planners off looking at the schematic and the phone rang just as I spotted an error. Turns out the customer was calling about the error I spotted. Planner wasn’t happy that a school kid found the error!

Thanks for the video, Ralph. I'm currently working on a PCB as well. How on earth do get frost at 18c? A UK phenomenon? Here in Norway, we are at 10c now but nowhere near frost :-)

Good Info on getting started on a PCB project. With 3D printers coming down in price, why don't you just custom design an enclosure to accommodate your display, pilot lights and other components, then just print it out on the 3D printer per your specifications? I'm sure you can get a lot of use out of the 3D printer for other projects. If would make for another good UKposts video.

What about swinging esp32 board around 180 deg. Put a hole in the side of the case for usb connection to reprogram and serial monitor.

I have followed your videos and now I thought I should try making my own PCB. I made a working prototype, created a schematic in EasyEDA, converted it to a PCB and routed. Actually no serious problems. But.. how do I select the components? Do I have to select the specific component already in the schematic? Even if I try to do that JLCPCB does not have them as basic. Most videos I watch just skip out the actual component selection. May be you can fill that gap in the future? Thanks for all your videos.

Hi Ralph, what about routed air gaps between the high and low sides of the PCB? I'm no electrical engineer and I don't know the best practices concerning them, but maybe someone can chime in on the subject?

The relay footprint looks very different to the HRM2-S relay. For a start your footprint is for a surface mount relay, not through hole?

The older red led color is so much richer than modern ones when not lit. They're almost like a translucent blood red

You could have used the metal case of the heater as the heat sink for the SSR. LOTS of metal.

I'm watching this a year after you've done it but I can't find the final video that shows what ever happened to this. Is there another one? I want to do this very thing... sort of. I want to put a wireless thermostat across the room from the unit and have a receiving circuit box that will cut off the mains to the heater at that point. Really it is not that much different from what your doing here I dont think. Is it??? Thanks.

Interesting video as always. But I see you need to add another plaything to your kit, a 3D printer. Its ideal for printing electronic enclosures. Put it on your Christmas list :-)

Yup tried using the back box and cover before both parts shattered!

Ralph! Don't you have a 3d printer for making enclosures? Or you are not able to use a cad program? I do most of my enclosures from a 3d printer.

A Bezel around the display hides hides errant saw/file cuts. Easy to 3D print.

How about a DIY SSR with zero crossing triac optocoupler driving a power triac and a flat stock strap of aluminum for a heat sink for the triac. Small and flat form factor you can slip in anywhere in that case. No moving parts to wear out also. I just don't trust those mini relays that say can handle such huge amperages.

Honestly I have seen so much madness going from schematic to PCB, that after a while I just started to design on the PCB editor and skip the schematic. With enough experience that becomes easier anyway. Schematics are really more for making it "official". Even creating the footprint is just "place pads and know your grid spacing".

Would have went for a triac and an optotriac with zero crossing detection for switching instead of a relay - way more robust for resistive loads.

Do not use a heat sink in a heater. You will sink the heat from the heater into the SSR. It is all about the thermal balance. If ambient of the sink is hotter than the junction, it will just heat up the junction. Rather than a good coupling you want thermal decoupling of the heater ambient and the SSR. If you would like to use that at all. I wouldn’t in this case (pun intended)

I would have totally made it temperature controlled directly connecting to heater element. You'd need a realtime uC, like 328p as well and SSR or triac though. Let me know if you want me to share a well tested AC PDM source code that you could use.

Your link to the case on Banggood does not work

What's your patreon link Ralphy?

A lot of great comments here, love reading what everyone is thinking.

hi

DANGER POTENTIALLY LETHAL DESIGN ! Ralph I am a UK sparks - you are wrong you NEED an earth. You are passing AC THROUGH the 'double insulated box' not containing it inside. Your design has lost the earth connection to the heaters metal enclosure. You are unprotected should a should a fault develop and the metal becomes live and you touch it!!!!. Just use 3core in for the incoming and outgoing and just join the earth wires inside your box with a terminal block or crimp(ideally). Additionally, you need to consider your fusing. You have 2 AC paths 1 heater & 1 PCB both sides need a fuse. Suggest you use an externally accessable panel fuse for AC heater. Don't forget the fuse in the plug doubles as protection for cable. So 13A in plug, 10A slow (glass) within box and 500mA (slow) glass, on PCB for electronics. Stick the snubber in for end/emi reason and also to limit radiated wireless emissions from arcing relay contacts, you still might have esp or even local wi-fi/radio connection issues