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I am a newbie to electronics, but I do have experience working with electrical wiring in the UK, so I am comfortable working with 240V reasonably safely. I have also built a camper including all the 12V electrics from scratch. I am fairly technically able, as a building physicist and academic researcher. However, my expertise is in mechanical engineering and physics rather than electronics or electrical engineering.

The Project

I am designing a new generation biltong box. My previous biltong boxes had electrical devices wired individually into plugs and then manually switched.

For those who dont know 'biltong' is the South African equivalent of US jerky. We simply dry the raw beef as opposed to light cooking.

enter image description here Image 1 - first generation manually switched biltong box

The first generation boxes worked great - they were a test bed for the physics - airflow/heat and drying rates. However, they lacked finesse and were technologically challenged. So I have set myself the goal of building a new smaller box, laser cut from acrylic and packed with more intelligence.

My inspiration is drawn from this great project

Technical details

The biltong dryer design currently comprises of:

  • 1no 240V AC 60W tubular heater - this one specifically. I might want to add another in the future.
  • 2no 12V DC 14.4W axial fans - these ones
  • 1no 12V LED strip light - not yet selected

What I want to do / Problem Statement

I would like to have an Arduino based system, to facilitate the following features:

  1. 2no temperature and humidity sensors (one at the inlet at the bottom and one at the outlet at high level)
  2. Touch screen to: 1. display temperature and humidity over time, 2. enable manual control of the heater, fans and LED light, 3. allow me to modify the temperature and humidity setpoints
  3. The ability for the Arduino to control the heater (on/off) and the fans (ideally variable) based on setpoints for temperature and humidity. But also to allow me to operate the heater and fans individually from the touchscreen - on / off / auto for all.

Please help

I know all the kit I am trying to control and how I want to do it (conceptually). Now I need some advice on how to make this happen please.

To kick things off I have purchased an Arduino MEGA 2560 board and kit and have experimented with a few small projects. I now want to use this to control the above.

Questions

  1. Is my idea sensible and achievable (technically)?
  2. I know that I will need a 240V relay to control the heater. Is this safe and reliable? ** This is my biggest concern. What can you recommend for this - there are so many available on the market.
  3. I think I will also need 3 more additional relays for the 2no fans and LED strip light. Is this the best way to control the 12V fans and LED light?
  4. Can I control the speed of the proposed 12V fans? And how is this achieved?

Huge thanks in advance.

First Edit

My calculated current for the heater is 60W / 240V = 0.25A

Questions:

  1. So for a SSR - this looks like a good option - what do you think?
  2. Found a four channel, four route MOSFET - what do you think? Once I have the switching working, i will consider working out the PWM. But switching will be fine for now.
  3. How do I go about designing the circuitry - are there any good online Arduino resources for this?

Second Edit

enter image description here

Not sure where to go from here!

Also, cannot find MOSFET's in Fritzing.

closed as off-topic by Juraj, VE7JRO, sempaiscuba, gre_gor, Greenonline Nov 25 '18 at 12:09

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about Arduino, within the scope defined in the help center." – Juraj, VE7JRO, sempaiscuba, Greenonline
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 2
    It may be better to post your question on a different SE, like electrical engineering. Questions here need to be specifically about an aspect of Arduino programming. – MichaelT Nov 24 '18 at 14:47
  • Thanks Paul - can the MOSFET control the speed or do i need additional PWM module for that. Excuse the noob question. Please see the first edit in the original question where i have found some options, which I would appreciate some advise on. – Cairan Van Rooyen Nov 25 '18 at 9:04
  • Personally I do not feel it being on topic, basic electric control imho is on topic (As in, what component do I need from my Arduino to control x). Nor do I think it would be worth the hassle to close or move the question as it's perfectly answerable and has been already answered. – Paul Nov 25 '18 at 9:06
  • Regarding components, if it matches your requirements, they should be fine. I think you should separate it in smaller projects, first try controlling a single fan and then build on that. The mist simple designing tool is "Fritzing". – Paul Nov 25 '18 at 9:10
  • My biggest concern would be the touchscreen, the Arduino has quite limited processing power and interfacing a touchscreen can be difficult. However, if you purchase the screen from a source that supplies example code, tutorials and libraries (such as adafruit or other known vendors), you should be OK. Alternatively you can check if an 2x16LCD with buttons/'rotating knob' suffices as user interface. – Paul Nov 25 '18 at 10:30
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Is my idea sensible and achievable (technically)?

Yep, sure is. It's not really much different to a DIY Reflow Toaster Oven.

I know that I will need a 240V relay to control the heater. Is this safe and reliable? ** This is my biggest concern. What can you recommend for this - there are so many available on the market.

I would suggest an SSR instead of a mechanical relay. Easier to drive, and less electrical noise.

I think I will also need 3 more additional relays for the 2no fans and LED strip light. Is this the best way to control the 12V fans and LED light?

No. Use MOSFETs for those. You can drive those with PWM to change the speed / brightness.

Can I control the speed of the proposed 12V fans? And how is this achieved?

Yes - see above.

As far as control goes you may want to investigate PID as your calculation method.

  • Thank you for the advice. I have added an edit to the original post with some suggestions on possible devices. Would be grateful for any comments. – Cairan Van Rooyen Nov 25 '18 at 9:05
  • @CairanVanRooyen Yeah, looks OK. I use these SSRs in my reflow oven simply because they are easier to mount in a chassis than a PCB-based one.MOSFETs look fine. – Majenko Nov 25 '18 at 12:01
  • Thanks Majenko. All ordered, just got to wait for the postman! – Cairan Van Rooyen Nov 25 '18 at 13:46

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