Replacing transistor instead of Relay

[rezaf]

Hi.
I designed a circuit one year ago to control zoom and focus of security cam that installed on my robot(this cam's zoom and focus controlled with Positive and negative voltages)(and attached to post).
in this circuit the MCU controls ULN2003 and ULN2003 give + & - voltages to 3pin header with array of relays. the MAX232 make the +8 and -8 volts and give to NO of Relays. in pin header each pin of voltage have + or - with COM(or GND). for example if zoom pin of header is +8 with com pin, the camera get zoom+ &etc.

but now that I want to use my circuit again, don't have enough free space for relays and want to use transistor instead of relays.
what part of transistor I can use for switch instead of relays(that don't change polarity of voltages)? Note that the output of ULN2003 is -5
Thanks.

 

[karesz]

Hi,
Are you sure pls that a transistor cicuit can be really smaller as a modern relay for these special application?
Some time ago, I applyed a microminiatur relay in a design, I would say; check it pls for your case_ maybe you will have enough place for that?
The type is Panasonic`s AGN2oo12, can switch max. 1A, 110V,or 30W_ has DPDT contacts, needs 100mW ... Thes is a really nice small product.
Newark 83F7123 $3.68
Farnell 3104783 avail:0
Arrow AGN20012 $2.07
Regards!
K.

 

[rezaf]

you said true this relays are really small an nice and My Relays are 16x20mm.
but I don't think to find this relays in markets.
any transistor idea?

 

[karesz]

Hey,
Panasonic as Japan vendor isnt so far from Indonezia_or?
Otherwise you can search for "Opto-MOS", optocoppler with MOSFET as transistor, they has AC & AC/DC (called uni/bipolar) versions too...
If you will build it, you need 2x antiparallel connected MOSFETs + driving, it need not less surface as a miniatur Realy!
Otherwise, you can find lot of other relative small & good relays, most from Panasonic, but from some other USA vendors (& maybe China) too.
Do you have Farnell,Newark or other Distributor? They hes some similar miniature relay surly in program...
K.

 

[IanP]

It looks like the camera doesn’t need much current to operate focus and zoom ..
Any general purpose transistors that are rated for >15V and current >50mA will work ..
Eg. P100, N100 ..

Usually focus/zoom lenses operate independently form the camera, and that means that you can set COMMON voltage for zoom and focus anywhere you like ..
If that’s the case with your camera I suggest that create virtual ground at 6V and then drive focus (or zoom) from a half-bridge configuration (1+NPN and 1xPNP): to drive focus CW => 12V, to drive focus CCW => 0V ..
(no need for ULN2003 and MAX232) ..

IanP