In 2001 I bought a UV exposure unit for making PCB's from a local supplier. For what it was, it was rather over-priced but to make matters worse, it had a mechanical timer. The results from this were never consistent and I soon learned that exposure time is VERY important.
Several years later I "hacked" the unit and built-in a very basic electronic timer. I was never very happy with it but it did the job; until a couple of months ago when it started acting up.
As with many ad-hoc type projects that you decide to start on a weekend or over the holidays, you have to make do with what parts you have handy, and this was no exception.
I decided over the festive period that I would design a new simple timer unit to replace the current one; I would also add a couple of features that I've come to realise were missing from the original unit.
The one big missing feature is a warm-up timer. This runs the tubes for 5 minutes and allows them to warm up; cold tubes flicker and can affect the quality of the final exposure.
I decided to mount most of the electronics externally to the UV unit for a couple of reasons.
The only transformer I had was a little on the large size and would take up much of the internal free space.
Several years later I "hacked" the unit and built-in a very basic electronic timer. I was never very happy with it but it did the job; until a couple of months ago when it started acting up.
As with many ad-hoc type projects that you decide to start on a weekend or over the holidays, you have to make do with what parts you have handy, and this was no exception.
I decided over the festive period that I would design a new simple timer unit to replace the current one; I would also add a couple of features that I've come to realise were missing from the original unit.
The one big missing feature is a warm-up timer. This runs the tubes for 5 minutes and allows them to warm up; cold tubes flicker and can affect the quality of the final exposure.
I decided to mount most of the electronics externally to the UV unit for a couple of reasons.
The only transformer I had was a little on the large size and would take up much of the internal free space.
The picture above shows the main PSU and driver PCB mounted. The PCB contains a transformer, 5v regulator, rectifier, and support capacitors. It also contains a relay and driver transistor. This means that ALL the mains stuff is located on this one PCB and mounted securely inside the earthed metal box. At the top left of the picture you can see a small connector that I've mounted. This connects the PSU PCB to the main control box that will be mounted on the top of the unit. There is a cover that fits over the fuse on the PSU PCB that is missing from this picture.
Only three connections are required from the PSU PCB to the control unit; +5v, GND and the relay switch signal.
Only three connections are required from the PSU PCB to the control unit; +5v, GND and the relay switch signal.
The above image shows the control box mounted in place.
There is a display that shows exposure time remaining and a beeper to attract attention. The buttons are "STOP" to switch off the UV tubes immediately, "WARMUP" that switches the tubes on for a pre-programmed five minute delay, "INC TIME" to increment the exposure time (in 5 second increments) to a maximum of 300 seconds before re-setting back to 30 seconds, and "GO" to start the exposure and countdown.
I decided to build this as an integrated unit BUT you could build this as a self-contained external device so that you could use it to control the UV unit without any modification. It could also be used as a dark-room exposure timer or any other countdown timer.
At the heart of the electronics is an 18F25K22 PIC programmed in AMICUS BASIC. This means that you can simply change the firmware for your own needs if required.
I'll publish the design for this when I get time.
There is a display that shows exposure time remaining and a beeper to attract attention. The buttons are "STOP" to switch off the UV tubes immediately, "WARMUP" that switches the tubes on for a pre-programmed five minute delay, "INC TIME" to increment the exposure time (in 5 second increments) to a maximum of 300 seconds before re-setting back to 30 seconds, and "GO" to start the exposure and countdown.
I decided to build this as an integrated unit BUT you could build this as a self-contained external device so that you could use it to control the UV unit without any modification. It could also be used as a dark-room exposure timer or any other countdown timer.
At the heart of the electronics is an 18F25K22 PIC programmed in AMICUS BASIC. This means that you can simply change the firmware for your own needs if required.
I'll publish the design for this when I get time.
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