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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 25 June 2006, 22:18 PM Post subject: ZX24 based SMT Reflow Toaster Oven |
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I've been experimenting with a reflow oven built using a toaster oven and have gotten good results with it. The oven is a small convection toaster oven that can often be found at a good price on eBay (search using the keywords EuroPro TO289). The oven has two heating elements (one on top and one below) and a fan for circulating the air to achieve more even heating. It will accommodate boards up to about 8.5x11 inches in size but I have used it primarily to reflow several smaller boards at once.
The attached file contains ZX-24 source code for the PID controller along with an ExpressPCB schematic and board layout (2.5"x3.8"). Although the controller software uses hard-coded temperature profile parameters, the controller board has the provision to add a 3x4 matrix keypad that would allow run-time entry and/or adjustment of the parameters.
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mikep
Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX
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Posted: 25 June 2006, 22:58 PM Post subject: Re: ZX24 based SMT Reflow Toaster Oven |
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| dkinzer wrote: | I've been experimenting with a reflow oven built using a toaster oven and have gotten good results with it.
The attached file contains ZX-24 source code for the PID controller along with an ExpressPCB schematic. |
Nice. After manually soldering SMD parts, I think I'm ready to try solder paste.
I think you need a total of 21 I/O pins:
- 7 for Parallel LCD
- 2 for thermocouple
- 2 for fan and heater control
- 1 for buzzer
- 2 for switches
- 7 for keypad
Therefore I think you can reduce the component count and complexity by utilizing a ZX-44, ZX-40 or even a ZX-24e (when available).
It might also be useful to use the red/green LEDs on the ZX24/ZX24e to show when the heater and fan are on.
It might be nice to at least separate out the temperature profile into a data array loaded from program memory. I expect that individual tuning it required for different toaster ovens.
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 26 June 2006, 0:44 AM Post subject: |
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Actually you only need a single analog input for the thermocouple. The AD595AQ outputs an analog signal proportional to temperature.
My constraints for this board were to have it be no larger than 2.5" by 3.8" (so it qualifies for the ExpressPCB MiniBoard service) and to use all through-hole components (for ease of assembly). You could meet the first constraint with a ZX-44 but not the second. I think it might be difficult to fit a ZX-40 in the small board area but it might be possible.
It is certainly true that the temperature profile control parameters could be separated out into a data array. It is likely that only the target times would need to be changed to adapt to a particular oven. The temperature and dwell parameters may need to be adjusted for different solder pastes.
I believe that many/most commercial reflow ovens use infrared heaters. I have seen a few infrared toaster ovens but ones with the standard resistance heating elements are much more common on eBay. You should be able to get a Euro Pro TO289 for well under $20 (not including shipping) if you're patient.
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mikep
Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX
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Posted: 26 June 2006, 1:06 AM Post subject: |
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| dkinzer wrote: | | Actually you only need a single analog input for the thermocouple. The AD595AQ outputs an analog signal proportional to temperature. |
True but there also seems to be an alarm connected to PC3.
| dkinzer wrote: | | My constraints for this board were to have it be no larger than 2.5" by 3.8" (so it qualifies for the ExpressPCB MiniBoard service) and to use all through-hole components (for ease of assembly). You could meet the first constraint with a ZX-44 but not the second. I think it might be difficult to fit a ZX-40 in the small board area but it might be possible. |
Given those constraints a ZX-40 and associated circuitry probably wouldn't fit but a ZX24e would especially with the removal of the I2C circuitry and 2 PCF8574As.
That also explains why the SSTs are not on the same board.
BTW I like to use tall female headers to plug a LCD into then I don't have a "dangling" LCD display. It works better when the LCD has a 1x14 connector rather than a 2x7 but you still need a standoff for the other side of the display.
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stevech
Joined: 23 Feb 2006
Posts: 657
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Posted: 26 June 2006, 3:34 AM Post subject: |
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Don - nice work.
No silk screen from ExpressPCB mini-board service?
I saw that you had done a lot to create that in the PCB design.
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 26 June 2006, 3:50 AM Post subject: |
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| Quote: | | No silk screen from ExpressPCB mini-board service? |
That's correct - neither silk screen nor solder mask is included in the MiniBoard service. That's the biggest disadvantage to using that but it is a quick turn and relatively low price. There is only a small amount of work to prepare for a production run with silk screen and solder mask.
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DH*
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Posted: 26 June 2006, 10:47 AM Post subject: |
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| dkinzer wrote: | | Quote: | | No silk screen from ExpressPCB mini-board service? |
That's correct - neither silk screen nor solder mask is included in the MiniBoard service. That's the biggest disadvantage to using that but it is a quick turn and relatively low price. There is only a small amount of work to prepare for a production run with silk screen and solder mask. |
I haven't used ExpressPCB for several years. If you have software that can create Gerber files, you can get high quality boards with solder mask (both sides) and silkscreen (both sides), including corner notches for a few dollars more. Shipping does take a bit longer. http://www.ezPCB.com will make 5 boards for $50 plus shipping. For higher quantities, I prefer http://www.pcbcart.com. I've used both. Quality and service are excellent.
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DH*
Guest
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Posted: 26 June 2006, 14:49 PM Post subject: |
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| If the heatsink is for the LM7805, going to a regulated +5V wall transformer might free enough room to use the ZX-40.
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victorf
Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
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Posted: 04 July 2006, 10:12 AM Post subject: |
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Don,
I was looking at the schematic of the reflow over controller and I noticed that you have included a 10k pulldown resistor on the SerIn pin (2) of the ZX-24. Is this recommended? It is not shown in the system documentation.
Any enlightenment will be appreciated.
Vic
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