I'm a newbee here and i don't have a good knowledge of electronics. I'm making an rf transmitter receiver device with a couple of 5v rf rx/tx modules. The whole thing has to work on 2 AA Alcaline batteries (The two rf modules work on 5v and i have to find a way to power them from the two alcaline batteries). My main problem rimains on how to turn off the rf modules when i don't need them. I'll put the arduino to sleep for 1 minute every other minute and i need to turn off those devices for that time. I thought it's better to use n channel mosfets agains transistor as i saw that with transistor there's a voltage drop. Can anybody suggest me a mosfet which can work for this project?
Technical parameters of the transmitter head
1.Product Model: MX-FS-03V
2.Launch distance :20-200 meters (different voltage, different results)
3.Operating voltage :3.5-12V
4.Dimensions: 19 * 19mm
5.Operating mode: AM
6.Transfer rate: 4KB / S
7.Transmitting power: 10mW
8.Transmitting frequency: 433M
9.An external antenna: 25cm ordinary multi-core or single-core line
10.Pinout from left → right: (DATA; VCC; GND)
Sorry for my ignorance. For high-side switch you mean the mosfet between the load and + power supply?
What would consume less between a pnp and a p channel mosfet?
To turn off a p channel mosfet or a pnp i will have to provide a high voltage. But after awhile when the batteries will start to loose power they won't provide the high voltage needed to turn it off. So it would be a problem right?
Yes, "high side" means between the positive supply and the load.
A MOSFET will lose less power.
To turn off the P-type MOSFET, you need to raise its gate to close to the same voltage as the source terminal (the one connected to the positive supply.) Use a pullup resistor and then you can use an N-type MOSFET to pull down the gate when you want to turn on the P MOSFET. When it's off, virtually no current will flow through the pullup resistor as the gate is an insulator.
You dont need to do anything for the transmitter apart from holding its data pin low, as they draw no current when not transmitting.
For the receiver whatever method you use it needs as close as 5V as you can get.
We still haven't talked about the issue of powering the whole thing from 2 alkaline batteries (3V) when you're using a 5V receiver and transmitter.
The easiest solution here is to throw those crapola receivers in the bin - the common green ones are junk. Poor range, and they require a full 5V to get vaguely acceptable performance.
These are a drop-in replacement, but work great at 3v and are dirt cheap:
I tested every kind of cheapo 433mhz OOK transmitter and receiver I could get my hands on last fall - these receivers easily bested the competition, even the $7~10 ones, and the $40 one I got from a US manufacturer.
The cheap green transmitters work fine at lower voltages, including off 2 alkaline batteries (I tested down to I think 2.4v or something - basically until the microcontroller stopped working) - I found little difference in range among the transmitters I tested.
I'd run it with a standalone arduino (or pro mini with the regulator and power LED removed), direct off the 2 batteries. Use a P-channel MOSFET to turn on/off the receiver (note - you can also unsolder the WAKE pin, bend it up so it doesn't contact the pad it was soldered to, and connect that to an IO pin on the micro; drive that pin low to turn on the receiver). The transmitters do not need the power to them shut off - I've got remotes running off 2 AA batteries and aggressive power management that have not needed new batteries since I assembled them last winter, and I've got the power connected to the transmitter continually.
DrAzzy:
We still haven't talked about the issue of powering the whole thing from 2 alkaline batteries (3V) when you're using a 5V receiver and transmitter.