PDA

View Full Version : Does this exist?



Oldbitcollector (Jeff)
03-24-2007, 09:28 AM
I'm no electronics engineer, so I thought I look for some experts..
Does this chip in the attached image exist?

Oldbit

T Chap
03-24-2007, 09:34 AM
That is similar to a Darliington array(typically used for shorting a circuit to GND, not passing analog or logic levels). Look up ULN2803. There are analog switchees too that resemble that. Another option is a DC solid state relay switch. The simplest vesion of that is a 4016 or 4066, with dozens of similar devices. The opto very much isolates a circuit, as well as a solid state relay(opto based).

Oldbitcollector (Jeff)
03-24-2007, 10:12 AM
Ah, ok.. Now I've got some terms I can work with... SSR.. Makes my day.. I just need to find one that will take a 5v input and I'm good to go.

Thank you!

Oldbitcollector

T Chap
03-24-2007, 10:26 AM
What is your goal?

www.opto22.com/site/pr_cat_sc.aspx?qs=100310071003 (http://www.opto22.com/site/pr_cat_sc.aspx?qs=100310071003)

The link has any kind of SSR you can imagine, AC, DC, depending on what you are trying to do there may be better options.

Oldbitcollector (Jeff)
03-24-2007, 10:58 AM
Actually, thanks to you, I'm looking at the 74HCT4066. It looks almost perfect.

I'm going to use an 80's microcomputer with 5v interface to control my Propeller inputs. I wanted something the will isolate the two units, yet allow the switch type inputs on the propeller. The 4066 appears to be it. I looked at the Darlington (I've got a couple) and I just couldn't achieve the isolation I needed with it. Inexperience perhaps...

Oldbitcollector

T Chap
03-24-2007, 11:07 AM
Why not just run the 5volts into the Propeller through a 1K? You can also isolate/interface the 5V stuff to 3.3 with a 4050, put 3.3v on Vdd of the 4050, but you can hit it with 5 volt levels on the input, and it will output 3.3 on the outs.

Oldbitcollector (Jeff)
03-24-2007, 11:23 AM
I was looking at the idea of just using 1K resistors off the output lines of the older machine and then connecting them directly to the Propeller pins, but was uncomfortable about how I should tie the grounds together, or if I should tie them together at all. Is there any ground potential damage that could happen to either circuit as a result? Sorry if this is an newbie question.

Oldbit

T Chap
03-24-2007, 11:40 AM
You should have all the grounds tied together, as there could be a differential and one boards logic levels could be higher by easily 10 volts in some cases, depending on the supplies. A 1k is fine, some use higher, like 4.7k, this is OK to do and is common. There are clamping diodes on each Propeller input that hold the input to 3.3 if the current is not too high, which is what the resistor accomplishes. It is usually the current that does damage, so when you limit or restrict it with a resistor, there is less possibilty of damage. There are some cases where the potential exists for unusual spikes or even short circuits off the board, in those instances more isolation is a good idea. But, for just running logic levels between boards, as long as the ground is tied, it is not a problem usually.

Oldbitcollector (Jeff)
03-25-2007, 02:41 AM
THANK YOU!

I feel like I truly learn something.. I've got several gaps in my understanding of electronics I'm working on, and you just filled in one of them.

Thanks again.

Oldbit