SparkFun Forums

[alumniu]

What I need:
This may be a fairly easy project for a student or hobbyist looking for some extra cash this holiday season. I am looking to commission someone to build a professional looking and operating (PCB) printed circuit board, provide a blueprint/ diagram of the board, and a component source list with pricing.

Payment / Delivery:
My budget is $50-125, depending on your final product. If awarded the task, I will pay you $50 for your efforts no matter what, with a possible $75 extra depending on your final product. Unless the completed project is deemed grossly unacceptable, you will earn the full extra $75. Payment will be made through PayPal upon arrival of your package. If you’d like, I can pay you for the necessary parts up front if you provide me with the parts list with sources and pricing. This amount will be deducted from the initial $50 you will receive. However you can still receive the $75 bonus depending on final product. Your final product should ship within 10 days of project acceptance.

Overview:
Circuit board whose intention will keep an 11” x 11” x 3.5” steel box at or around a temperature of (99ºF +/- 2%). Installation environment of the PCB will be inside an 18ga. steel box – screwed onto metal or plastic standoffs. Safety around humans and animals is a concern, which is why I would like to use AC to DC adaptor operating at a lower voltage/amperage. I am aware that you are the one with the knowledge of electronics, so if you have any suggestions or recommendations, it would be welcomed.

Component/Functions:
1. PCB size shall not exceed a size of 3” x 4” x any thickness.
2. Switch/sensor that will automatically turn OFF heater when it reaches upper temp limit.
3. Switch/sensor that will automatically turn ON heater when it falls below lower temp limit.
4. 6” long leads with an attached 2” or 3” fan.
5. 6” long leads with an attached red LED that will be recessed into the box’s cover.
6. 6” long leads with an attached black plastic toggle switch. Switching this on will turn on the fan, LED, and heater.
7. 6” long leads with an attached black plastic push-button timed switch. Attached to this will be a timed heat feature (possibly with a second heater, or maybe just one more powerful heater?) that will quickly bring the box up to temperature within 15min, and then turn off automatically. The switch and push-button can operate in conjunction, but should also be able to operate independently from one another.
8. The temp sensor(s) may need to be at the opposite end of the board that the heater(s) are located in order to minimize sensors from prematurely turning off without heating the entire box to desired temperature. This may not be completely necessary because the fan will help disperse the heat.
9. Box will use an AC to DC power adaptor switching from 110VAC to 12VDC- 1A or 24VDC- 6A. (May need your recommendation on this)

Looks do count- please don’t submit a grease-smudged circuit board with sloppy solder, or hand-written diagram on a cocktail napkin. Digital files are a plus but not absolutely necessary. I primarily use a Mac Pro computer, and have the capability of opening any Adobe program, as well as Solidworks files on my PC. If you are aware of a digital format that industry professionals use, than that would be the best, and I will find someone who can open the file for me.

Wrap Up:
I don’t mind paying a fair price for this first prototype board, however my intentions are to put this board into a production environment in the future- so keeping the actual production board cost as low as possible is a consideration. All components should be off-the-shelf. I encourage you to contact me with questions about my project. If in doubt, just email me and hopefully I can convey my intentions. Some aspects of the project may be expendable or flexible.

I am an honest, hardworking recent college grad, whose main job is in an unrelated field to this project. I am doing this in an attempt to make extra cash down the road if this project ever pans out for me.

[leon_heller]

Such a narrow temperature range will require PID control, and much more work than you have assumed.

[alumniu]

Thanks for the helpful reply Leon. I've posted this on other forums with less than kind replies. So I appreciate your advice. This is one of those areas of my project that could be flexible in order to reduce cost. I'm not sure what a more acceptable temperature range would be, but I would think I could allow for as much as 25% gain. I wouldn't want to go that far down in temp tho. Maybe 90 degress? Does that sound more reasonable?

[alumniu]

Also, from what I've read on other forums, I may be asking alot here. I'm looking for a hobbyist or student who would happy to earn some extra cash for their hobby and perhaps keep my costs low. That being said, terms are negotiable as far as compensation, time allowed, and up-front payment. I'm open to offers and appreciate your help.

[n1ist]

$50 will likely not cover the PC board and parts. Even perf board and parts would be tough. And that doesn't include design time and programming. Also, for 10 day turnaround, the $50 wouldn't even cover expedited processing and shipping for the board and parts.

The design issue isn't with 99 degrees, it is with the +/- 2%. That's what needs the PID control (ie, a processor and programming). Will the box be insulated or do you need to hold the temperature with varying ambient losses?
You mention a 15 min "fast" ramp rate but don't mention the slow rate. I haven't run the numbers to see if 12W is enough power (12v, 1A). 144w (24v, 6A) should certainly be able to do this.
/mike

[alumniu]

Thanks for the advice. So much more kind and helpful than the other forums. Is there a way to eliminate the need for a processor and programming to cut down on costs? I think I should probably start much smaller for the first prototype, and them maybe after some testing, ramp up to a PCB and fine tune it. How can I keep my costs low, while retaining the basic operation. The box will be insulated, so ambient loss shouldn't be a notable factor. Would making it on a breadboard be cheaper than perf board? Sorry for intermediate questions...noob here.

[alumniu]

or, given my initial budget. Would it be reasonable to just have someone design it for me and provide a parts list- and build it myself?

[rmteo1]

It is all about man-hours. To do this on a shoestring budget, the approach taken by most people is to develop the necessary skills (by treating the process as a hobby initially) to do everything themselves. The only downside is that even a relatively simple project like this can take a long time going this route. Here is an example of a very similar project - it took the developer over a year (excluding any initial learning period) to get it to the point where it could be turned into a commercial product. A student or hobbyist is unlikely to have that kind of time and/or resources to devote to this.

A professional developer can probably design it in just a few hours, but by the time you get all the stuff (including mundane things like board layout, firmware development, documentation, etc.) done you are looking at easily 40-60 hours of work. At $125/hour (what I charge for my services) you are looking at $5,000-$7,500 plus prototyping materials at cost (figure an additional 20%).

[alumniu]

That looks way more complicated that I was hoping to make this. I was thinking something more like this:

[jremington]

You don't need a PCB. As other posters have mentioned, small PID controllers have been available for years that do exactly what you want. All you have to do is select the controller and match up a suitable heater and a temperature sensor. The fan might not be necessary. Here is Omega Engineering's overview to their products, which are of very high quality (and expensive) http://www.omega.com/prodinfo/temperatu ... llers.html

However, you can get used and new PID modules on ebay for typically less than $50 US.
For example, try http://www.ebay.com/sch/?_nkw=pid%20tem ... 0924554265

[stevech]

OP skipped the "make vs. buy" step!

[alumniu]

It looks like the PID controller will provide the functionality im looking for, but i was hoping it wouldnt be so obtrusive. I saw the 1/32din models, but even that seems like it may be overkill with the display. I was basically hoping to redesign the circuit in the image above to keep it simple.

[Polux rsv]

As a starting point, you should look for "reflow oven controller". These units interface with small oven to use them as reflow unit. Everything is already there: controller, display, sensor interface, button, power supply, etc...

Some links I found:
http://www.sparkfun.com/products/81
http://www.rocketscream.com/blog/2011/0 ... ontroller/
http://danstrother.com/2011/01/15/reflo ... ontroller/
and lots more.....


Angelo

[lyndon]

I'll second, third, whatever the response to consider off the shelf PID temperature controls. There are some companies that make small heaters with the controller embedded (Minco comes to mind). You have received a few very good responses that are exactly on point, so I just wanted to add another voice in that direction.

This is not a simple project; a simple temperature controller would be something that would maintain temperature +/- 10F with an on/off thermostat type control. And even then there's no way I'd go near this project for anything less than 10x what you're offering. The cost of the individual steps adds up very quickly. I've taken on projects from online forums like this and charged less than half the going rate because it was a fun little job to help someone out. However, if you're looking for professional output, you need to be prepared to pay professional rates, or learn to DIY.

If you said: "just use an Arduino to control a heater that I've already selected," then it becomes more reasonable at 10x your offer. But at $125 max to do what you're asking, even if I were a starving student I'd run screaming. I'd make more money flipping burgers.

[alumniu]

I only want a simple project, with a simple temp controller maintaining temp +/- 10F with an on/off thermostat type control. Very similar to the photo above. My initial post was what I would ultimately like in the end i guess.