I have asked this question elsewhere and one person suggested using a mosfet, but other research states mosfets run slower than BJT transistors.
Here's the details of my question.
I own an HM-TRP radio module which I want automatically configured using just a microcontroller (at89C2051) and an external 5VDC power supply (USB). In the past I can successfully detect when the module is successfully configured for operation at a specific speed on initialization just by reading the magic string.
Now the problem is complex.
The only two ways I can tell if the radio module is at the correct speed are either a) wait for a remote unit to transmit data at the same speed, which in this case is never, or b) detect the magic string.
So the way I can achieve this is to somehow control the power supply programmatically so that the microcontroller guesses the correct speed (by setting serial mode 1 and playing with the timer reload values) and have it turn on the radio module. If after several hundred milliseconds, the magic string doesn't appear, then microcontroller needs to shut the radio module off and change the timer reload value so that its on a different baud rate.
I have no problem with doing this in software, but I was wondering if my schematic is correct for this purpose. In my previous circuits, I had the 3V power supply directly wired to the LM1117 3.3V regulator (IC3) so that the radio module stays on while the rest of the circuit is powered. Now I want to allow the microcontroller to completely switch on and off the power at its will.
Is the PN2222 NPN transistor ok for this purpose? If so, then what about resistor values, does the collector pull-up resistor need to be in the low hundreds ohm range to give the radio module enough power? Or should I use another part in place of the PN2222? and if another part, what should it be? can it be a part that's commonly available in stores?
P.S. The 74HCT04 inverters are used to help turn the 5V signals from the micro to the 3V signals for the radio module itself. I'm not sure if they can also be used to power the radio module as well. The radio module accepts a max of 3.9V.
Now could I get away with using a 2N2222 transistor and resistors or do I really need a mosfet? because afaik, I own zero mosfets. I own tons of transistors tho.
Here's the details of my question.
I own an HM-TRP radio module which I want automatically configured using just a microcontroller (at89C2051) and an external 5VDC power supply (USB). In the past I can successfully detect when the module is successfully configured for operation at a specific speed on initialization just by reading the magic string.
Now the problem is complex.
The only two ways I can tell if the radio module is at the correct speed are either a) wait for a remote unit to transmit data at the same speed, which in this case is never, or b) detect the magic string.
So the way I can achieve this is to somehow control the power supply programmatically so that the microcontroller guesses the correct speed (by setting serial mode 1 and playing with the timer reload values) and have it turn on the radio module. If after several hundred milliseconds, the magic string doesn't appear, then microcontroller needs to shut the radio module off and change the timer reload value so that its on a different baud rate.
I have no problem with doing this in software, but I was wondering if my schematic is correct for this purpose. In my previous circuits, I had the 3V power supply directly wired to the LM1117 3.3V regulator (IC3) so that the radio module stays on while the rest of the circuit is powered. Now I want to allow the microcontroller to completely switch on and off the power at its will.
Is the PN2222 NPN transistor ok for this purpose? If so, then what about resistor values, does the collector pull-up resistor need to be in the low hundreds ohm range to give the radio module enough power? Or should I use another part in place of the PN2222? and if another part, what should it be? can it be a part that's commonly available in stores?
P.S. The 74HCT04 inverters are used to help turn the 5V signals from the micro to the 3V signals for the radio module itself. I'm not sure if they can also be used to power the radio module as well. The radio module accepts a max of 3.9V.
Now could I get away with using a 2N2222 transistor and resistors or do I really need a mosfet? because afaik, I own zero mosfets. I own tons of transistors tho.
