Design optimisation - Schottky diode array

[cadman97]

that would be great.

Thanks

[cadman97]

if I pick up all the components for the 32 input module that synthex posted. I should have all I need for the 22 input updated module, correct? Planning on heading out today to see what I can get.

[Synthex]

if I pick up all the components for the 32 input module that synthex posted. I should have all I need for the 22 input updated module, correct? Planning on heading out today to see what I can get.

What do you mean by that : "the 22 input updated module" ?

[cadman97]

you had stated earlier in the post that you would kindly redesign the 22 input analog board with this chip, but if I build the new one you posted in the other topic. would the 22 inputs work untill we get a firmware update?

[Synthex]

you had stated earlier in the post that you would kindly redesign the 22 input analog board with this chip, but if I build the new one you posted in the other topic. would the 22 inputs work untill we get a firmware update?

No, the new PCB design 32 inputs will not work with the 22 inputs firmware !

[Kartman]

Why use schottky diodes at all when with a small modification, you can use much cheaper 1n4148 diodes? For the positive rail diodes, you need to drop the reference voltage by one diode drop below vcc - one diode, a resistor and a capacitor. This would ensure the multiplexer input does not saturate. Alternately, raise the VCC for the multiplexer one diode drop above VCC.

I'm perplexed why you're persisting with through hole components and getting pcbs made for this? Surface mount stuff is quite easy to hand solder using a normal soldering iron. The board I designed for Aaron was soldered using solder paste and a gas powered soldering iron with the hot air adapter. I prefer to use a soldering iron, solder and some flux gell. The pcb I designed was wonderfully simple as far as pcbs go - the design just fell into place.

Heres how to solder surface mount by hand:

for small components like capacitors and resistors:
1. put small blob of solder on one pad on pcb
2. get tweezers, pick up component and place it whilst heating the pad with the solder blob on it
3. solder other pad

For fine pitch components like the processor:
1. use tweezers and magnifying glass to locate the component on the pads
2. when in position, tag one pin with the iron and a little solder
3. tag the opposite pin with the iron and a little solder
4. make sure the component is located correctly, if not, heat pad and relocate
5. get solder gell - usually comes in a small syringe. put a small amount all over the pins
6. get soldering iron . put a blob of solder on the pins and wipe gently across the pins with the soldering iron
7. flux stops the solder joining pins
8. repeat for four rows of pins
9. use magnifying glass to inspect for shorts. use soldering iron to fix any shorts. you can tap the board whilst the solder is hot to shake off excess.
10. use flux cleaner to clean board.

With a little practice it becomes fast and easy. You can practice on old PC motherboards - use a hot air gun to remove the ics and try to resolder them using the above process. The trick is to be quick and not to heat the pad up too much. If you muck it up, let it cool and retry.

You can see the results on Aaron's board.

[Aaron]

I'm perplexed why you're persisting with through hole components and getting pcbs made for this? Surface mount stuff is quite easy to hand solder using a normal soldering iron.

maybe not for you cause your a genious - but to the average person who has not had much experience soldering even thru hole could be difficult.

Please note the opinions expressed by Kartman are not endorsed nor otherwise affiliated with Aaron in any way.
These comments are personal opinions, and do not necessarily represent the views of the cadre or otherwise.

[mgd49]

Hi there,
I bring this topic back, because I found it 'by mistake' and I think that the 74s1053is a very good alternative solution to bags of Bat85.

But! when I look at its datasheet, it says that it's supposed to be supplied with 1.3v. How do you handle this when most of the components are 5v 'compliant' ?

thanks so far,

[ignotus]

I built a MD board years ago using those diode arrays. Works fine. Here's the board layout I used if you want to have a look at it.

[ignotus]

Though on second thoughts, if you're going to build it yourself, it makes much more sense to just use SN74HC4851 multiplexers and skip the Bat85 diodes or arrays altogether.