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Forum Index : Microcontroller and PC projects : Maximite 2012 !!
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| pito Newbie  Joined: 09/06/2011 Location: Posts: 25 |
..Have a look at FST3253, fast, cheap, used in sdr radios as a mixer till 50MHz.. ..you need a switch with low internal resistance/impedance.. Pito |
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Nick Guru  Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Thanks. I've downloaded the datasheet and will look into whether I can use it. |
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donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Ashurley both Mick and myself have both had open heart surgery. It was all that smoking and drinking I did for 30 years, which I gave up about 20 years ago. Now they can re-bore my plumping, slap me on the head like in a Benny Hill sketch, and tell me what a good boy I am, then give me another 20 years before my next service, if I behave myself. My car doctor won't give me that. If I took a poll on you lot, we may all end up in the same Benny Hill sketch. :-) Walking frames, wheel chairs, and the Benny Hill theme song, all running around in circles in a park. Oh, and young nurses, we must have sexy young nurses. Cheers Don... https://www.dontronics.com |
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sparkey Senior Member  Joined: 15/06/2011 Location: AustraliaPosts: 819 |
from sparkey tripple heart by pass thre years ago 14 angio grams 6 thaliiums and 7 stents technicians do it with least resistance |
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| donmck Guru Joined: 09/06/2011 Location: AustraliaPosts: 1313 |
Struth Brian, and I thought I was crook. I feel a lot better now :-) Cheers Don... https://www.dontronics.com |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Had a look at that FST3253 Dual 4:1 Multiplexor/Demultiplexor Bus Switch but unfortunately (if I've understood the datasheet correctly) it won't do the job. Here is the Logic Diagram and Truth Table from the datasheet... 
It looks as though it will channel 1 channel (there are 2) into *1 of 4* outputs. This chip will allow me to route the VGA to either Red, Green or Blue..but only one at a time. That's only 3 colours. I need a bit more flexibility to route the 1 channel to at least 8 combinations, example... to RED and GREEN only, to GREEN and BLUE, to all RED, GREEN and BLUE, etc. This will allow me 8 colours (including BLACK). Have I read this incorrectly? If so, any other suggestions for a substitute chip? |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
they dont let you die: :they make you grow old;;;;; technicians do it with least resistance |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
use two chips or even three.... technicians do it with least resistance |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Ah yes. They're cheap enough I suppose. Let me go back to my corner again and give it some more thought. :) Would a 74LS139 Dual 1 of 4 decode/demultiplexer be used? I know it's for digital circuits but since the VGA output is essentially digital (may need something to bring it to 0-5v spec). Where's the best place to find the FST3253? |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
just looking at that ls139 it has two sets of inputs and dual outputs it may do it but im only sumizing i guess you have looked at the data sheet ..ls should be fast though technicians do it with least resistance |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
I think it will be fast enough. I'm just wondering if the FST3253 is more likely to work with the VGA signal directly whereas the LS139 requires the signal to be 0-5v (digital). Who do you recommend to get the FST? Jaycar don't seem to have it. |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
I wonder, since all I'm wanting to do is decide where the single VGA signal in going to 1 of 3 inputs, would an old 4116 Quad Bilatereal Switch do the job? |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
you could try "rockby electronics in melb" of farnell will prolly have it i would try both..regards ..or maybe even "RS Components i just looked at wes they dont seem to have it give that a go or even just google it... technicians do it with least resistance |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
74hc139 will be faster technicians do it with least resistance |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
if you want the "fst3253 "looks like your going to have to get it of the net ...rockby no farnell no dont know about rs components or even radio parts group ...but i did find it when i googled it technicians do it with least resistance |
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| sparkey Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 819 |
isint a 4116 a ram chip technicians do it with least resistance |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Yep. A typo. 
I meant a 4016 I'm going to give it a try. |
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stuarts Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 199 |
Nick, check out the specs of the 4066 as well, I seem to remember one of them was faster, but I cant remember which. Stuart Time is nature's way of keeping everything from happening all at once. |
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| Nick Guru Joined: 09/06/2011 Location: AustraliaPosts: 512 |
Thanks Stuart. I see that the 4066 has lower ON resistance which will be better than the 4106 (300ohm). I'll pick one up at Jaycar including the required IDC connector. |
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| pito Newbie Joined: 09/06/2011 Location: Posts: 25 |
@Nick, a hw guy always google few numbers higher and lower to find better version of the chip  - so have a look at fst3251 (8:1) or fst3257 (4x2:1).. It seems the 3251 is the best fit for you.. P.
PS: SN74CBT3251 - TI TC7MB3251FK - Toshiba FST3251 - Fairchild 74FST3251D - ON Semiconductor PS1: mind you are going to drive a low-impedance load with the MUX (unless you will use a driver), so you need a switch with an on-resistance ~5-10ohm max.. PS2: 3251 is bi-dir analog/digi switch so it will work 1:8 as well.. PS3: not sure you need a "mux" actually - as you need something like 1:(bin combination)_of3bits MUX only if you intend to modulate somehow the signal (many levels of r-g-b). For 8 colors you need 3 bits anyway (for the 8 color combinations) passing directly to the VGA r-g-b pins, maybe tristated.. The idea of "multiplexing one maximite video output to a _comination_of_r_g_b_on_the_VGA_connector" is equivalent to direct passing the 3 rgb_mux_control_bits to the VGA connector as the actual "color code"... It means in order to show 8 colors all you need are 3 bits to be passed directly to vga pins (with some sync modulation as it is today), as a binary 0x000, 0x001, .. 0x111, not as 1:(one of 8 combinations) as this is the same, except you have to have a resistive network connected to the mux, and, moreover, one more pin needed (1-output from maximite, 3 for mux combinations). You cannot avoid the need for passing 3bits info out of the chip when you require 8 colors even linewise.. |
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