Multiple MOFET on one chip? Or circuit alternative

Falcon

Hello,

I'm using this circuit as the basis of a leak detector that are 15-30' from a BS2:

I have four of these on a breadboard to detect leaks at four different locations and its taking up lots of space. I suppose the higher sensitivity of the MOSFET helps overcome the lenth of wire between the detectors and the BS2.

Is there a chip available that combines four (or more) MOSFETs into one discrete package to minimize the circuit?

Is a MOSFET overfkill for this purpose? Would any other dicrete device perform the same purpose but in a smaller package? OP AMP maybe?


I've seen the Conductivity Sensor on page 131 of Applied Sensors v1.4 but I really just need a reliable Go/No Go type of device vs. a degree of conductance.

falcon

PJAllen

Well, you don't need a big honking 511 for this.
There are smaller FETs available, logic-level jobs, TO-92: VN2222L, BS170, 2N7000

Phil Pilgrim (PhiPi)

An IRF511 is certainly overkill in that app. You don't need a power MOSFET in a huge TO-220 package. You can get MOSFETs adequate for the job in the much smaller TO-92 package (e.g. 2N7000) and dual MOSFETs in smaller-yet SMD packages.

-Phil

erco

You could even use a small SCR for that. If you're just triggering and alarm/beeper, you might not need a Stamp, as an SCR will latch on once triggered. They are extremely sensitive and could easily be triggered by your water-gap switch.

Falcon

I appreciate the responses.
These four leak detectors actually feed the 74HC165 circuit found on page 150 of Stampworks v2.1. I figured the 511 might be overkill but that's what the circuit (found on page 112 of Matt Gilliland's The Microcontroller Application Cookbook 2) called for.

I'll take a look at that those T0-92 packaged FETs.

Thanks,

falcon

Tubular

I've found IRL6372's useful due to their low gate threshold.

These are 2 N channel fets in an SOIC-8 package for 30~60 cents. There are lots of "dual" variants in exactly the same SOIC-8 package

Tracy Allen

You could use CMOS gate chips that have 4 or 6 in one 14-pin package. The threshold is Vdd/2. Just about any would work, CD4011, CD4001, CD4050, or the 74HC or 74HCT equivalents. A CD4093 with its Schmitt trigger inputs would give a nice snap action. Isolate the sensor itself from the gate with a resistor, placed close to the transistor, in order to forestall ESD damage to the gate.