Mamu' tactile switch question
- Thread starter Skyfntm
- Start date
- th_trl_thread_readers 0
- Status
Im not sure that can be done due to the amp limits on the switch. I could be (and probably am, lol) wrong. Would cool to know though. I love those little switches.
the cheesy, simple answer is: buy one of the MV cheapo kits that use 14500 cells: there is a small pcb, instructions, a switch, and a mosfet. Just use the electronic parts and toss the other parts in the emergency-parts-bin.
I have read some things that leads me to beleave it can be done. I think you use a 320 resistor or something like that. But I don't know and I want to know lol.
I'm sorry but if I wanted the "cheesy simple answer" such as you put it I would not have posted this topic. But I did post this so I must want to know how I can do this. That is if it possible. K thanks
Hey Sky, it is a MOSFET you want, this lets you use underrated switches. That cheesy simple answer is actually a good one and those instructions from madvapes will explain a lot. They should be available on their site as well.
Sent from my Nexus 4 using Tapatalk 4
Sent from my Nexus 4 using Tapatalk 4
skyfntm,
You can't use that switch on a mechanical mod. The switch she uses has a very low amp limit, and must be used with a mosfet. A mosfet is a kind of ciurcut that would control the amprage. so to amswer your question NO don't try and use one it will fry in about 2 seconds at the amprage draw of the battery.
peace
mick8844
You can't use that switch on a mechanical mod. The switch she uses has a very low amp limit, and must be used with a mosfet. A mosfet is a kind of ciurcut that would control the amprage. so to amswer your question NO don't try and use one it will fry in about 2 seconds at the amprage draw of the battery.
peace
mick8844
Thanks asdaq. This is the answer I was looking for. And now the "cheesy simple answer" has an explanation to it which makes it the "easy route" to my question.
Now we are getting moregooder! Would you happen to have a schematic for wiring this with a strait bat mod?
I learned how to use that 3103 correctly here Raidy gave the diagram he is a member here. It works for touch or tact switches but it is wired wrong and unprotected.
Original post check page 14
Original post check page 14
hum......tactile switch thread is moving into mosfets.....interesting discussion...
Last edited:
Below is some info on using a mosfet to make a switch. Most of the below information came from DrMA when he helped me on a project.
"I'm usually of the opinion that N-channel MOSFETs make better switches, because they tend to have lower resistance [RDS(on)]: i.e. low-side switching. Assuming you'll be using just one LiPo (nominal 3.7V) when picking a FET to work with, look for one a VGS(th) <1.5V, enough current to support your application +50% [ID(on)] so it doesn't overheat, and appropriate breakdown voltage (VDS > 4.2V)
Here's a very nice and easy to understand guide: Using the Power MOSFET as a Switch - MOSFET Switching
Here's the basics of FET switching:
- use N-channel FETs to switch the ground (low-side switching). Gate needs a pull-down resistor for OFF, and gets connected to the (+) side of the batt for ON
- use P-channel FETs to switch the (+) connection (high-side). Gate needs a pull-up resistor for OFF, and gets connected to ground for ON.
In general, P-FETs have higher resistance than N-FETs.
In a P-channel FET, current flows and gets switched in the direction Source->Drain. The body diode is reverse biased with respect to S->D
In contrast, for a N-channel FET, current flows and gets switched in the direction Drain->Source. The body diode is forward biased with respect to S->D
The resistor is used to bring the Gate potential to reference when the switch is off. It also functions as a current-limiting resistor when the switch is on, so you don't short the battery. You want the highest resistance value that accomplishes a full off state with the switch open. You'll need to play with the resistor value to get the desired results. I'm guessing it would be between 10K and 50K. This is where a variable resistor comes in really handy."
Here are some simple diagrams that DrMA provided and then I added some info.
Low-Side (negative) Switching using a N-Channel MOSFET.
High-Side (positive) Switching using a P-Channel MOSFET.
"I'm usually of the opinion that N-channel MOSFETs make better switches, because they tend to have lower resistance [RDS(on)]: i.e. low-side switching. Assuming you'll be using just one LiPo (nominal 3.7V) when picking a FET to work with, look for one a VGS(th) <1.5V, enough current to support your application +50% [ID(on)] so it doesn't overheat, and appropriate breakdown voltage (VDS > 4.2V)
Here's a very nice and easy to understand guide: Using the Power MOSFET as a Switch - MOSFET Switching
Here's the basics of FET switching:
- use N-channel FETs to switch the ground (low-side switching). Gate needs a pull-down resistor for OFF, and gets connected to the (+) side of the batt for ON
- use P-channel FETs to switch the (+) connection (high-side). Gate needs a pull-up resistor for OFF, and gets connected to ground for ON.
In general, P-FETs have higher resistance than N-FETs.
In a P-channel FET, current flows and gets switched in the direction Source->Drain. The body diode is reverse biased with respect to S->D
In contrast, for a N-channel FET, current flows and gets switched in the direction Drain->Source. The body diode is forward biased with respect to S->D
The resistor is used to bring the Gate potential to reference when the switch is off. It also functions as a current-limiting resistor when the switch is on, so you don't short the battery. You want the highest resistance value that accomplishes a full off state with the switch open. You'll need to play with the resistor value to get the desired results. I'm guessing it would be between 10K and 50K. This is where a variable resistor comes in really handy."
Here are some simple diagrams that DrMA provided and then I added some info.
Low-Side (negative) Switching using a N-Channel MOSFET.
High-Side (positive) Switching using a P-Channel MOSFET.
Last edited:
Below is some info on using a mosfet to make a switch. Most of the below information came from DrMA when he helped me on a project.
"I'm usually of the opinion that N-channel MOSFETs make better switches, because they tend to have lower resistance [RDS(on)]: i.e. low-side switching. Assuming you'll be using just one LiPo (nominal 3.7V) when picking a FET to work with, look for one a VGS(th) <1.5V, enough current to support your application +50% [ID(on)] so it doesn't overheat, and appropriate breakdown voltage (VDS > 4.2V)
Here's a very nice and easy to understand guide: Using the Power MOSFET as a Switch - MOSFET Switching
Here's the basics of FET switching:
- use N-channel FETs to switch the ground (low-side switching). Gate needs a pull-down resistor for OFF, and gets connected to the (+) side of the batt for ON
- use P-channel FETs to switch the (+) connection (high-side). Gate needs a pull-up resistor for OFF, and gets connected to ground for ON.
In general, P-FETs have higher resistance than N-FETs.
In a P-channel FET, current flows and gets switched in the direction Source->Drain. The body diode is reverse biased with respect to S->D
In contrast, for a N-channel FET, current flows and gets switched in the direction Drain->Source. The body diode is forward biased with respect to S->D
The resistor is used to bring the Gate potential to reference when the switch is off. It also functions as a current-limiting resistor when the switch is on, so you don't short the battery. You want the highest resistance value that accomplishes a full off state with the switch open. You'll need to play with the resistor value to get the desired results. I'm guessing it would be between 10K and 50K. This is where a variable resistor comes in really handy."
Here are some simple diagrams that DrMA provided and then I added some info.
Low-Side (negative) Switching using a N-Channel MOSFET.
High-Side (positive) Switching using a P-Channel MOSFET.
Please forgive my ignorance, but what is the 47k going from 1 on the battery to the gate? And if possible could you explain how, what, why you would use this and also how you would determine you need this. Thanks
It's a resistor and DrMA explained it pretty well here "The resistor is used to bring the Gate potential to reference when the switch is off. It also functions as a current-limiting resistor when the switch is on, so you don't short the battery. You want the highest resistance value that accomplishes a full off state with the switch open. You'll need to play with the resistor value to get the desired results. I'm guessing it would be between 10K and 50K. This is where a variable resistor comes in really handy."
Bapgood you rock. If you could define the "desired results" you are trying to achieve that would be great. And also how you figure out what resistor you need. Thanks
"You want the highest resistance value that accomplishes a full off state with the switch open."
So you want the highest resistance value resistor that still allows the mosfet to "shut" when the tactile switch isn't pressed.
I think this should be my last question, how do I determine that the resistor has allowed the MOSFET to shut off?
Button pressed = Battery voltage......Button not pressed = 0 voltage
I figured this was the method the method but I just want to know this was the method. Thanks again Bapgood. And I lied I have one more question
is there too much when it comes to the resistor?- Status
