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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Xamiche on April 10, 2008, 06:42:12 AM
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I'm just about to order the parts required to build the below circuit, however there is one component I am not familiar with. It's the TL1 component in the circuit. I'm wondering if any of the electronics savvy members can tell me what it is?
(http://i107.photobucket.com/albums/m301/aaronlittle/Cd32_joy_tl1.jpg)
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It's just an RF suppression choke. It provides a high impedance to RF signals (looking at the image, I'd estimate from around 50MHz upwards).
To cut a long story short, it isn't necessary for the circuit to work. TL1 reduces emissions from the circuit above a certain frequency, and provides some immunity from RF radiated into the connecting cable from an external source. From a design point of view, it seems strange why you'd include this into one of the external lines, but not the others.
I'd suggest not fitting TL1. But it's usually good design practice to fit a 1nF (or whatever) ceramic capacitor between each external signal line and ground, close to where the cable enters the PCB.
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Many thanks for the reply and advice Castellen. :-)
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i think it acts together with 470p capacitor as LC band rejection filter
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I'm thinking I'm going to include the component in the circuit. Only thing is, I'm not sure where to find it in the electronics catalogue I use. I buy from Altronics Australia generally, although they don't always have what I need.
Edit:
Any Australians here know of a good source of electronic components? I've tried a couple of places and none seem to carry any 74LS165s.
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Have you triede JayCar or Dick Smiths? If you get them in WA.
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Tried Jaycar, no joy there. I'm not sure if Dick Smith still sells those type of components. They're more an appliance/electrical store these days. Last time I was in Dick Smiths I had trouble getting caps and resistors, much less chips. I sure miss the Dick Smith and Tandy of old.
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You can use "high speed" 74xx equivalent, like 74ALS165, 74S165 or 74HCT165.
For the "strange" component: it is a ferrite with 6 perforations, dimensions in the schematics (diameter 6mm, 10mm in length).
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rkauer wrote:
You can use "high speed" 74xx equivalent, like 74ALS165, 74S165 or 74HCT165.
For the "strange" component: it is a ferrite with 6 perforations, dimensions in the schematics (diameter 6mm, 10mm in length).
Ahh cool. It never really occurred to me to look at using the ALS or HC 74s. Thanks :-)
Regarding the ferrite component, am I likely to find this at a regular electronic component store? I've scoured my Altronics catalogue and cannot find anything remotely like it.
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Or there's equivalent CMOS gates you can use (4000 series) which will do the same job. They tend to have different pinouts, but nothing that 30 seconds with the datasheet can't resolve.
Either that, or do the same job using different logic. You can just as easily use combinations of NAND or XOR gates to exactly the same job. If you can't work it out in your head, then just write out the truth tables.
Regarding the inductor, the author hasn't even specified the type of ferrite to use (there are various different componds which react differently at different frequencies). So the value of inductance vs frequency clearly is not important. If you really want to put an inductor in there for whatever reason, just select any low current 100µH leaded inductor. It's not going to make any difference.
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Actually, I still have lecture notes on a shift register we built with flip-flops back in digi electronics. Time to do some revision I think :-D
Thanks for the advice all. :)
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f=1/(2*pi*sqrt(L*C))
so ie. for 1MHz band filter it will be T1L=54uH