4 replies to this topic

[optimus primer]

listed below is what i am reading on the pdf. page 12. this might not be enough information for you but then again it might.

if the netduino board can not handle that much current would i be able to add resistance to the line in return lowering the voltage so that reads below 20mA for alarm and even lower for standby?

 

what i am trying to do is make a functional security system using the honeywell key pad with my netduino. i want to keep all the function of the security keypad. so correct me if i am wrong. but with the current listed below if i program the netduino to light up an led with the alarm set and the sensor breaks connection would it work? and not light up the led if the keypad is set for standby and a sensor breaks?

 

 

 

 

DEVICE CURRENT # UNITS TOTAL CURRENT

 

6148 Fixed-Word Keypad 30mA standby/55mA alarm

[optimus primer]

listed below is what i am reading on the pdf. page 12. this might not be enough information for you but then again it might.

if the netduino board can not handle that much current would i be able to add resistance to the line in return lowering the voltage so that reads below 20mA for alarm and even lower for standby?

 

what i am trying to do is make a functional security system using the honeywell key pad with my netduino. i want to keep all the function of the security keypad. so correct me if i am wrong. but with the current listed below if i program the netduino to light up an led with the alarm set and the sensor breaks connection would it work? and not light up the led if the keypad is set for standby and a sensor breaks?

 

 

 

 

DEVICE CURRENT # UNITS TOTAL CURRENT

 

6148 Fixed-Word Keypad 30mA standby/55mA alarm

here is the website that the i got the information from above from.

 

http://www.alarmhow....tion Manual.pdf

[hanzibal]

I'm not quite sure what you're trying to do but I believe those numbers to be the power consumption of the keypad when in standby and alarm state respectively. Even if the keypad is able to drive these currents on its outputs there's no danger reading them since whatever load you connect will only draw a maximum current equal to the voltage across it divided by its internal resistance. When configured as inputs, digital pins of Netduino are high impedance, meaning they have a very large resistance and therefore, virtually now current go into them. If you want to drive a load using a Netduino output pin, it's very much different since the Netduino can only source 20mA on any single pin and some 200mA in total (if remember correctly). To drive higher currents than that, you should use a transistor (or MOSFET) to handle the load. In this mode, the Netduino only controls the base of the transistor which requires only a small amount of current to "open" the transistor and let current flow between the collector and emitter. You connect the load between the powersupply and the collector and the emitter to ground (on an NPN type transistor). Normally, you also put a resistor on the base to limit the base current (maybe 2 - 10k or so) but it's usually not critical. The Netdunio can drive most LEDs directly since these will generally glow nicely with a current of only 5 - 10mA.

[optimus primer]

im fairly new to the netduino and or programming together. what i am thinking is that the power runs thru the security keypad and when the alrm is set that the amps will indicate that the alarm is on and if a sensor break that it trigger the led(alarm).

 

i have bought the keypad but it has not got here yet. not really sure how the thing works yet. but when i get it. i be able to tinker with it and can give a more clearly question.

 

 

thanks,

[hanzibal]

Aha, you wan't to exploit the current shift to detect the alarn going off. I suppose you could do that with a hall effect sensor. Snce the difference is rather small you probably have to design som kind of digital filter in software to avoid false alarms due to momentary current increases that I suspect will occur now and then.

You would typically place the sensor close to the power line going into (or out of) the keypad and use the Netduino ADC to sample the output of the sensor which should be proportional to the current of the keypad. You'd have to some how calibrate the samples according to actual current levels.

EDIT: Here's a nice video explaining the difference between different types of hall effect sensors and also show how to use them:


Oh, and in case you didn't know, a wire carrying a current will create a magnetic field around it. The larger the current, the stronger the magneric field which you can then mesarue using a metric ratio type hall effect sensor and explained in the video.