Need Circuit Design -- Cheap...

I applied a 66/33 duty-cycle, so the original circuit fails, as I predicted. The third page shows the new circuit behavior with 66/33 applied, but the pot adjusted for average value at "TT1" as VCC/2.

...Jim Thompson

OK, So I will draw up the second design and get the parts for it first and give it a go.

Will post drawing of actual parts / pin outs, this is more of just a sanity check for me to ensure I and interpreting your drawing correctly.

Alas, the wife is "making" me go help our new neighbor now, won't be back to this for a few hours. I get to move furniture around and re-wire his phone connedtions, the prior owner had 4 lines! One for each kid, and when the telco hooked him up they did not connect the internal lines all to the new live line so he only has a few jacks working, that should be easy enough, it is the furniture I am not looking forward to...

Aga>>

What? A _guy_ who can't move his own furniture around ?:-)

I only help people who really need it... new _babes_ in the neighborhood ;-)

...Jim Thompson

Hi Jim, OK, I think we are there, I have redrawn your schematic to the actual parts and like before I think I have all of the right parts and connections, if you could do a quick compare I would appreciate that to ensure I interpreted your drawning correctly.

With the new parts I am just going to stick with what you specified, so that other questions are off the table.

This leaves me with one question, you have the Input Signal from the LED going through 2 inverters, U2A & U2B, just out of interest sake I was wondering why, if you inverst something twice don't you just end up with the same thing you started with?

Thanks!!

PS Upon your reply I will put in the order. I am glad you took the iterations to refine this so I did not have a bunch of orders to Digi-Key.

Tomorrow. Dinner time.

Quick glance... lower relay, how does it get +5V for the coil?

With no load specs for you controller, I was reluctant to load it down with a resistive (read: current) load.

...Jim Thompson

When I looked up the parts at Digi-Key there were a lot of nubmering methods, none had any that just started with "74HCxxxx"

MM74HC02N-ND MM74HC02N

TC74HC02AP-ND MM74HC02N

SN74HC02N-ND SN74HC02N

CD74HC02E etc...

Any usggestions, or is there a better place to go? I like Digi-Key even though I generally pay more than like Goldmine, but I can usually get every part I need from one place and the cost difference is generally very small compared to shipping charges from 5 places, not to mention my time.

I am very sorry to hear about your son, my Step mom, all 4 grandparents, well you get the idea,I will make the donation in his name.

Thanks

Thanks -- Good catch -- I updated the drawing.

Also changed the CD to SN parts. Also in another post asked you what the difference was between all of the various letters in addtion to the part number meant, I did no mean for you to explain every variation, but if you could suggest a specific part number. Please not that just a "74HCxxxx" does not seem to exist at Digi-Key, they all start with like "SN74HCxxxx" or "MM74HCxxxx" or "CD74HCxxxxx", the best I could make out is it was brand differences.

Same URL: (Relay powered now)

Thanks

First 2 letters appear to be just the manufacturer, though "CD", in the past, suggested voltage capability higher than 5V.

MM=Motorola SN=TI

...Jim Thompson

Still wrong :-(

...Jim Thompson

Third Time the charm I hope... Must be getting tired, should be right now.

Thanks again...

I ordered to parts, had a real scare when a 10pF cap looked like it was $43.00, but a 0.01uF was 50 cents. Hope I did the conversion right, since I bought the 0.01uF cap. Weird how they were priced like that. Total parts came out to $23.00 including chip sockets and a perf board from Digi-Key.

Parts should be in by the weekend and I will put it together then.

Don't forget to ground the unused gate inputs. ;^)

That's right. 74HCxx is the generic number.

(Watch the wrap and parsing.)

Since I had my usual "relaxing" Monday lunch, could someone else check my work (John F ??)

Points...

Never leave CMOS inputs floating

Value correction

Polarity correction

Like I say, since I had my usual "relaxing" Monday lunch, could someone else check my work (John F ??)

Australian lurker... saturation problem solved (over "relaxing" lunch)... will clean up schematic and send tomorrow morning ;-)

...Jim Thompson

I didn't see an answer from Jim on that question, so: U2A & U2B form a non-inverting buffer so the uc is not loaded down.

Ed

Keerect. I did post such a statement earlier.

...Jim Thompson

Thank Jim, Another great catch on the cap value mistake!! Also tied all of the unused inputs on the inverters and gates to +5DC, and addedd the line on the second 555C between trigger and threshhold. I corrected the LED direction also (that is already in the alarm circuit, I just drew it wrong...)

I take it the outputs are fine to float?

One other thing, many messages back you said the two electrolytics caps could be ceramics if I could get them, is that still the case, I actually just ordered 2 of each and planned to use the electrolytics as shown in your circuit, but now that I went back to review everything I noticed that comment from you, is there a preference for the two 1uF Caps? (I will have both types)

I have made the corrections and reposted the image under the same address:

The Corrected one from Jim: (BTW -- You need to add the "(ThomasSCH)Mark-Up.pdf" to the URL if your does not. I use agent and the URL ended at the ( mark...

Thanks again, we should know this weekend if it works, well you might already know, but I will know...

Thank you also for double checking Bob,

Ground them or tie them to +5VDC, Jim has them shown all tied to +Vcc, in this case +5VDC?

I have made the corrections noted by Jim and reposted the image under the same address:

The Corrected one from Jim: (BTW -- You need to add the "(ThomasSCH)Mark-Up.pdf" to the URL if your does not. I use agent and the URL ended at the "(" sign.

Thanks aga

Hi Jim, On the cap C1, 1uF electrolytic, in an earlier post I asked if a ceramic would be ok and I think you said it would be better if I could find one, well I did, but since I am double and triple checking the details, should I use the 1uf electrolytic or a 1uF ceramic for C1, I ordered both.

Also, Bob suggested that I tie the unused inputs to ground, your corrected schematic shows them going to Vcc (+5VDC), which is correct?

Thanks

Either way is fine. Just don't float.

...Jim Thompson