Slightly OT: Video Buffer / Amp / Driver ?

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Tim036

Member
I'm building a 8 channel Video switch using a HCF4051B IC as the switch.

Now the signals, in part, are from a Broadcast Satellite Receiver.

The Switch is controlled by a Picaxe.

Now the snag is that it must drive drive two identical video channels .

Anyone know of an (low cost) IC that can act as a driver?

The idea is to connect the output of the switch to the input of this driver IC and send the identical video signals on their way !

Or would a simple transistor emitter follower do the biz ? If so any suggestions for the transistor ?

Tim
 
V

vttom

Senior Member
Tim036 said:
I'm building a 8 channel Video switch using a HCF4051B IC as the switch.

Now the signals, in part, are from a Broadcast Satellite Receiver.

The Switch is controlled by a Picaxe.

Now the snag is that it must drive drive two identical video channels .

Anyone know of an (low cost) IC that can act as a driver?

The idea is to connect the output of the switch to the input of this driver IC and send the identical video signals on their way !

Or would a simple transistor emitter follower do the biz ? If so any suggestions for the transistor ?

Tim
Click to expand...
Since it looks like you're probably dealing with NTSC or PAL composite video signals rather than super high-frequency HDTV-type signals, you can probably split and re-drive the MUX output with a pair of generic NPN (2N2222) emitter-followers just fine.

But if you want an application-specific IC, Google for "video distribution ic" or "video line driver ic" or something to that effect.

I also recommend that you terminate each of the 8 inputs with a 75 Ohm 1% tolerance resistor, and decouple with a capacitor (not sure of a good value, 100uF seems like a good starting point), into each channel of the analog MUX IC. You don't want to terminate between the output of the MUX and the input of your driver because the impedence of the MUX channel will probably not be a very good match to the expected 75 Ohms.

Ideally, you'll want a +5/-5V power supply so you can DC bias the output followers @ ~0V. If you only have a single-ended supply, you can use a "virtual ground" of VDD/2 instead.

Oh... 1 more thing. If you keep looking, instead of a generic analog MUX, you can find application-specific IC's that are designed for this purpose, with a re-drive amp built right in.
 
hippy

hippy

Ex-Staff (retired)
If you are looking for broadcast quality you're going to have to be careful with choice of components and board layout. There's a reason studio kit usually costs an arm and a leg.
 
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Tim036

Member
vttom said:
Since it looks like you're probably dealing with NTSC or PAL composite video signals rather than super high-frequency HDTV-type signals, you can probably split and re-drive the MUX output with a pair of generic NPN (2N2222) emitter-followers just fine.

But if you want an application-specific IC, Google for "video distribution ic" or "video line driver ic" or something to that effect.

I also recommend that you terminate each of the 8 inputs with a 75 Ohm 1% tolerance resistor, and decouple with a capacitor (not sure of a good value, 100uF seems like a good starting point), into each channel of the analog MUX IC. You don't want to terminate between the output of the MUX and the input of your driver because the impedence of the MUX channel will probably not be a very good match to the expected 75 Ohms.

Ideally, you'll want a +5/-5V power supply so you can DC bias the output followers @ ~0V. If you only have a single-ended supply, you can use a "virtual ground" of VDD/2 instead.

Oh... 1 more thing. If you keep looking, instead of a generic analog MUX, you can find application-specific IC's that are designed for this purpose, with a re-drive amp built right in.
Click to expand...
Sound advice ! Thank you ! I need two identical outputs so a 2N2222 seems a good way forward.


Many thanks.

: )))

Tim
 
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tiscando

Senior Member
Off-topic threads

So basically, off-topic threads on this forum are about something that is not picaxe-related, but it may be (going to be) interfaced by the picaxe.

Another example is an off-topic thread by ArnieW about a contrast problem with a non-picaxe LCD that is (going to be) interfaced by a picaxe.

Thanks for your answer ;)
 
hippy

hippy

Ex-Staff (retired)
On-topic are matters which directly relate to PICAXE.

Off-topic are those which are completely unrelated to a PICAXE.

Then there's that murky area between, where there are degrees of relationship with a PICAXE, particulary aspects of a project which involve a PICAXE but may not directly be a PICAXE issue.
 
T

Tim036

Member
vttom said:
Since it looks like you're probably dealing with NTSC or PAL composite video signals rather than super high-frequency HDTV-type signals, you can probably split and re-drive the MUX output with a pair of generic NPN (2N2222) emitter-followers just fine.

But if you want an application-specific IC, Google for "video distribution ic" or "video line driver ic" or something to that effect.

I also recommend that you terminate each of the 8 inputs with a 75 Ohm 1% tolerance resistor, and decouple with a capacitor (not sure of a good value, 100uF seems like a good starting point), into each channel of the analog MUX IC. You don't want to terminate between the output of the MUX and the input of your driver because the impedence of the MUX channel will probably not be a very good match to the expected 75 Ohms.

Ideally, you'll want a +5/-5V power supply so you can DC bias the output followers @ ~0V. If you only have a single-ended supply, you can use a "virtual ground" of VDD/2 instead.

Oh... 1 more thing. If you keep looking, instead of a generic analog MUX, you can find application-specific IC's that are designed for this purpose, with a re-drive amp built right in.
Click to expand...
Should anyone be interested:-


Much good advice here which I heeded !

The 2N2222 suggestions worked a treat.

I found the 100uF Electoytics worked fine,

I spit the 12V rail with a 7805 regulator, yielding -5 volts +7 volts

The Emitter resistor I chose was 330 ohms and to bias it to approx 0 volts I found a 4.7k resistor from base to the +7volt rail was all that was needed.

Quick and a tad dirty but works just fine.

The Maxim ICs tended to be too expensive as the competition was about 35p for an 8 way switch.

Many thanks to all that contributed to this thread !

: )))

Tim
 
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