I am trying to build a feedback circuit in which a drill blade touches a conductor at either 3.3 or 5V and the newly electrified drill bit, feeds current through a carbon brush from a DC motor into an off switch that districts current between the trigger assembly and the DC torque motor driving the drill. I'm pretty sure it's a 12V DC drill.
I have seen examples of TIP120 transistors that turn something ON when the digital pin goes high, but I cannot find a switch program or device that effectively acts as a low current circuit breaker, turning this higher voltage off. I looked at Power tail II but it is AC and bulky.
I am, of course, new to Arduino and need a decent amount of guidance if you have an idea.
I'm not clear what you want, but think of it as switching ON when the pin goes LOW. You will need a transistor to switch the motor on and off, but we can't tell you which one until you tell us
the voltage ("I think it's 12V" isn't precise enough!), and
the current drawn by the motor.
Both of these should be marked on the drill.
I'm using a medical device drill. Used in surgery. The manufacturer has told me is 15v DC and I'm waiting to see if they'll answer my questions regarding current. If they don't tell me, I guess I might have to break it to get a multimeter in there. Can you outline the basic idea before I do that? Burning up a few different transistors versus ruining this drill sounds preferable.
What about supplying power to the drill through a relay that is held ON by the Arduino and goes OFF when the contact with the wire is detected.
I suspect your bigger problem will be reliably detecting the contact quickly enough to avoid damage. I would be tempted to try a much higher contact voltage - 30v or 50v - as high as you can without risk of personal injury. Obviously you can't feed that high voltage direct to the Arduino pins so you will need an intermediate device or at least a couple of resistors to make a voltage divider.
Egonenglish:
I'm using a medical device drill. Used in surgery.
Is this a high speed medical drill? Cutting the power to one of those won't stop it immediately, as there will be some run-on, dependent on friction. Also, if this is to be used in a medical situation, it wouldn't be a good idea to use a carbon brush for contact, as bits of carbon could break off and get into the patient, and a carbon brush probably wouldn't withstand sterilisation.
The manufacturer has told me is 15v DC and I'm waiting to see if they'll answer my questions regarding current. If they don't tell me, I guess I might have to break it to get a multimeter in there.
Then how do you propose to turn it on and off? As long as you can get to the 15V leads you can measure the current with a meter.
It is a torque DC drill, and is designed to stop quickly. It doesn't carry momentum with the drill. I just need to feedback inhibit the circuit between the trigger assembly and the motor and the rest takes care of itself. I'm trying two back calculate the amp/hours of the battery and the amount of time the battery has before full discharge. It's like a Ryobi drill you'd get at a hardware store in most ways. Doesn't have to stop on a dime, but quicker the better.
The carbon brush would be outside the patient and fragmentation is not a major concern because it will be inside the housing of the drill if things work out the way I think they will
I've seen D3, LOW turn off higher voltage circuit with the TIP120 transistor. If I had say D4, HiGH turn off D3 and send it low, I guess that might work. I was hoping to reduce microprocessing or Boolean logic so the reflex shutdown was as fast as possible. Any thoughts?
Egonenglish:
I was hoping to reduce microprocessing or Boolean logic so the reflex shutdown was as fast as possible. Any thoughts?
The time it takes an Arduino to process some code will be utterly trivial compared to the time required to physically brake the motor. Don't worry about software optimization.
Prompt and reliable detection will be the challenge.
Can you reliably measure (as it stands) a voltage from the drill bit?
eg, a low/high signal either 0-3/5v?
if so, i don't think this is much of a problem to do, using a relay to switch between on and off (from the output of a transistor as it's signal) should be easy enough to achieve.
Yeah, I can pull enough current to light a red LED, so that's got to be close to 150mA. I was thinking an NPN transistor for the switch control. I'm trying to learn more about them. The trigger uses a simple push button, similar to the Arduino Uno reset button. I think I could patch my transistor between the push button and the motor.
I'm waiting for the carbon brush to arrive by mail, but I intend to pick up the charge off the rotating hub of the rounded drill bit base near the chuck.
Egonenglish:
Yeah, I can pull enough current to light a red LED,
Through what? From where?
so that's got to be close to 150mA.
A standard red LED will shine quite brightly on 1/10th of that and melt on 1/5th of that.
I was thinking an NPN transistor for the switch control. I'm trying to learn more about them. The trigger uses a simple push button, similar to the Arduino Uno reset button. I think I could patch my transistor between the push button and the motor.
Pictures and diagrams would help.
I'm waiting for the carbon brush to arrive by mail,
We're all waiting on some definite information, so that we don't have to guess what you're trying to do.