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Show"N"Tell ( Your Machines) / Re: A Wee Prober
« on: August 04, 2014, 06:52:08 PM »
So the probe is designed to work with an input using 5V with a 4k7-10k ohm pull-up or pull-down resistor, and the KStep requires 12-24V to power the 10k ohm optos. After a couple quick calculations, using 5V and a 4k7 resulted in the probe switching ~1mA, whereas even at 12V the optos would need ~1.2mA, or ~2.4mA at 24V. I was more concerned about the higher voltage reducing the probe life, so a solution was needed -
Strib board. The saviour of electronic bodges by mc_mtb, on Flickr
The board on the left is the solution, using what parts I had on hand. The end result is the probe having to switch ~0.9mA at 5V.
The solution could of been simpler, as I could of bypassed the optos, and used one of the 5V tolerant LVTTL inputs directly on the KFlop, however I prefer keeping logic power supplies seperate from control/machine wiring.
The board takes 24V, drops it down to 5V using a simple linear regulator, then uses a NPN transistor to switch the opto input to the KStep to GND, via the probe and a 4k7 resistor. I also added a couple LEDs, one so I know it's powered up, and one so I know when the probe circuit is complete. When the probe isn't active, the opto/input is active, so should a fault develop, the circuit should be broken and everything stops.
One little bodge I like, is the 7805 regulator should have a tantalum, mylar or similar low internal resistance capacitor mounted as close as possible to the input leads, when it is mounted at a distance from the power source. Now given I don't have any suitable through hole capacitors on hand, a solution was quickly found -
Mounted as closely as possible.. by mc_mtb, on Flickr
The only suitable capacitors I had, were surface mount ceramics, and you can't get any closer to the leads, than directly on them!
The capacitor is not big enough, so I coupled it with an electrolytic, which will handle the bigger ripples, and the ceramic should at least absorb some of the higher frequency ripples.
The other board on the right, was thrown together quickly to provide a basic breakout board to connect to the 26pin header on the KStep. After soldering on the header, I ran a thin dremel grinding disc between the two rows of pins. The 0.2" terminal blocks were spaced to allow access to the inner blocks, with the outer blocks staggered across one strip/0.1".
I ran out of time to get them mounted on the machine today, but it should be a quick job in the morning, along with putting the finishing touches to the probe holder, at which point probe testing can begin.
Strib board. The saviour of electronic bodges by mc_mtb, on Flickr
The board on the left is the solution, using what parts I had on hand. The end result is the probe having to switch ~0.9mA at 5V.
The solution could of been simpler, as I could of bypassed the optos, and used one of the 5V tolerant LVTTL inputs directly on the KFlop, however I prefer keeping logic power supplies seperate from control/machine wiring.
The board takes 24V, drops it down to 5V using a simple linear regulator, then uses a NPN transistor to switch the opto input to the KStep to GND, via the probe and a 4k7 resistor. I also added a couple LEDs, one so I know it's powered up, and one so I know when the probe circuit is complete. When the probe isn't active, the opto/input is active, so should a fault develop, the circuit should be broken and everything stops.
One little bodge I like, is the 7805 regulator should have a tantalum, mylar or similar low internal resistance capacitor mounted as close as possible to the input leads, when it is mounted at a distance from the power source. Now given I don't have any suitable through hole capacitors on hand, a solution was quickly found -
Mounted as closely as possible.. by mc_mtb, on Flickr
The only suitable capacitors I had, were surface mount ceramics, and you can't get any closer to the leads, than directly on them!
The capacitor is not big enough, so I coupled it with an electrolytic, which will handle the bigger ripples, and the ceramic should at least absorb some of the higher frequency ripples.
The other board on the right, was thrown together quickly to provide a basic breakout board to connect to the 26pin header on the KStep. After soldering on the header, I ran a thin dremel grinding disc between the two rows of pins. The 0.2" terminal blocks were spaced to allow access to the inner blocks, with the outer blocks staggered across one strip/0.1".
I ran out of time to get them mounted on the machine today, but it should be a quick job in the morning, along with putting the finishing touches to the probe holder, at which point probe testing can begin.