There is also be portions of the honey stick machine, including heaters and pump, that will need to be run on 120VAC and sill be switched on and off by the Phidgets interface.  Relays would be the simplest option here, but again these mechanical relays have a far less than desirable rated lifespan in number of cycles.   So I’ve opted to use solid state optically isolated AC relays.  They typically have a far lower amperage rating, but I only expect to drive a maximum of 0.5 amps presently on any given AC device.  The circuit pictured shows the very simply NPN driver circuit triggering an LED and the solid state relay.

One of the challenges in the circuit design that I was worried about was obtaining the additional outputs I expect to need for the honey stick machine.  The Phidgets USB controller only has 8 outputs and while I could simply add a 2nd Phidgets module, I’d really rather avoid the extra expense in the final model.  I had proposed using a 4 to 8 decoder previously to add the extra outputs.  The good news is that the 74259 addressable 8 bit latch works quite well and replaces the entire circuit proposed.  The bad news is that the 4 outputs from the USB controller aren’t guaranteed to update at the same time.  This means that random signals can be generated on the output.  Not a good thing.

The solution? An edge detection circuit on all 4 inputs to generate a pulse any time the input changes, a delay timer to debounce the multiple pulses sent when the inputs change at different times and a 2nd timer to send the all clear to the 8 bit latch signaling that it’s ok to look at the input signals now that they are stable.  The Phidgets controller updates the output signals approximately every 8mS, so it’s quite possible that when multiple inputs are changed that the change will occur over two consecutive updates.  So if you wait and look at what signals changed over 12mS (1 1/2 update cycles), you should catch any output that occurs over two cycles.  Or at least that is the theory.

It’s been about 12 years since college and since I’ve done any circuit design and I really don’t have access to the oscilloscopes , etc. needed to see really what is happening with the signals in the circuit.  Though I’m  happy to say that something must have stuck after 4 years of college, the circuit works flawlessly.  As long as I limit the software to sending out signals every 16mS , I can selectively turn on and off each individual output using just 4 outputs from the Phidgets controller.  This does have the downside that it will be slower and only one  output can be addressed at a time,  but many of the outputs needed are not  so time sensitive  so this should work well for them.  Those that are time sensitive can be driven by the remaining 4 outputs of the Phidgets controller directly.

It’s winter again, or at least it looks like it out the window.  We had several inches of snowfall Tuesday night and it looks like it’s going to stick around for awhile.  So it’s time to get back to the honey stick machine.  It’s been over a year now since I designed the simple MOSFET solenoid driver circuit, and I’ve finally constructed it on the prototype board and tested it. I’m happy to say it worked flawlessly.  It’s probably overkill for the lower power solenoids, but keeping them all the same (the project calls for 7 drivers) will allow significant flexibility.  This is good since I don’t know what I’ll get into once I get into the mechanical side of things.

The picture, from left to right, shows the power supply, Phidgets USB interface, and the prototype board with solenoid on the right side of it.

With a change of jobs and being in the middle of bee season, I haven’t had much time to devote to much else, including working on the honey stick machine.

I have noticed however that Dunbar Honey Farm is now advertizing their honey stick machine in the American Bee Journal for $1900  (Phone 586-770-9953).  I suspect this is the same machine he had a year ago when my wife talked to him.  If so, it is a relatively manual system  that uses a specially made pump, a holder for a dozen or so straws and an impulse sealer.  It certainly beats filling them individually with a syringe, but isn’t yet the automated machine I’m hoping for (though I’m sure it’s far cheaper).  If anyone finds out differently please let me know.