Conver TTL into Relay

[Buechsenschuetz]

ULN2803 is a good choice for a relay driver. You should add a diode in reverse direction in parallel with the relay coil to cut down excessive inductive voltage when the relay is switched off. 1N4148 will be suitable for low-power relays.

Anyhow, when using higher voltages to drive a relay the ULN2803 does NOT offer galvanic isolation and in case of a failure of this IC high voltage may get to the TTL output of your board. If you need better protection you should use a PhotoMOS relay as an interface. The input can easily be driven with any TTL output supplying (or sinking) 10mA and they will switch up to 50V/300mA on the secondary side, plus offering full protection against failure. The disadvantage is that you need one device for each output.

[K C]

The ULN2803 already has diodes for protection.

The only thing the originator needs to drive is a 5V relay, so no high voltage

[Buechsenschuetz]

It is true that the ULN2803 has integrated diodes. But to make use of them you have to connect pin #9 (COM) to the supply voltage of the relay. The clamp diodes will withstand voltages up to 100V min (the datasheet gives figures for reverse current at 100V).

When using the ULN2803 as relay driver keep in mind that the saturation voltage of the output transistors is rather high due to the darlington configuration and is up to 1.1V at 100mA. So the relay should have a "must operate" spec of 3.9V max. Some vendors offer relays with a slightly reduced nominal coil voltage of 4.5V which might be more suitable in this case.

[SandeshKesarkar]

HI KC!

Just returned from tour and seen yr messages.

Thnx for suggession.

I will try this and  get back to you in case of problems.

However if you have any experience on using USB cameras with Labview pl share How to define pixel value of camera as in normal streaming mode my camera is streaming at low pixel value of 320 X 240; where as if I snap it from camera I get 2016 X 1512.

How to change Camera Link file and snap the image at max capacity of camera?

Regards

Sandesh

[Dennis_Knutson]

Please create a new question for this because it is completely unrelated to your original question. You should also post to a more appropriate board (i.e. Machine Vision).

[michaeld]

Sandesh,

Please clarify, are you using a USB camera with the IMAQ for USB driver, or are you using a CameraLink camera? If this is a USB camera, you can use the IMAQ USB Init.VI to set the Video Mode input, and the options you will be able to access are largely dependant on your camera and driver itself. If you are using a CameraLink camera, you can define the size of the image to acquire in MAX by going to the Acquisition Parameters tab for your framegrabber.

[SandeshKesarkar]

Michield,

I am using handycam which has both USB and Cameralink port. However MAX is not detecting the camera may be b'cos I am not using any NI card but Microsoft card and for the same when I connect with Cameralink it takes microsoft driver and opens th image in 760 X 615 resolution. But may objective is to acheive max. resolution what camera can offer.


Sandesh

[michaeld]

Sandesh,

Since you have created another thread in the machine vision forum, let's keep discussion of this topic over there.

[topex]

Speaking of ULN2803, can i just ask what can be an alternative device if this array driver is not available in our market? It will be use as relay driver on the outputs of parallel port...

[K C]

Just a transistor and a protection diode will do fine.