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Ask HN: What are you working on?

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Re: Ask HN: What are you working on?

#102

Post by jgrahamc »

jacquesm wrote: post #3
jgrahamc wrote: post #2

I am working on making 500 of these: http://www.jgc.org/blog/2008/03/building-temperature-probe-f... for schools in Uruguay.

You can possibly get rid of the pair of 9V batteries by using a floating ground that you make with two resistors.

Agreed. I am redesigning it for the production version. I'd like to pull everything from the USB if possible.

Re: Ask HN: What are you working on?

#104

Post by dkuchar »

http://www.lendfriend.net - friends and family lending site built in ASP.NET MVC & jquery. I wasn't the first one to come up with this, but I got the idea after I funded my first startup on credit cards, had some friends with money, but didn't want to complicate things with a DIY loan.

We're launched, but we have a lot of work ahead of us. If anyone has any ideas/suggestions/criticisms please let me know.

Re: Ask HN: What are you working on?

#105

Post by paulreiners »

mtinkerhess wrote: post #14

I'm writing an iPhone musical instrument with an emphasis on just intonation (as opposed to equal temperament). http://en.wikipedia.org/wiki/Just_Intonation http://en.wikipedia.org/wiki/Equal_temperament

I wrote a just intonation library in Java, if you're interested:

http://sourceforge.net/projects/leipzig/

Re: Ask HN: What are you working on?

#106

Post by jacquesm »

jeromec wrote: post #99
jacquesm wrote: post #62

Earlier quoted context omitted.

The midpoint voltage of the voltage divider used for the reference is 0.45V, well within the -2.5 to +2.5 swing. The reason why I think it matters is that batteries are a nuisance, they run empty and will cause a problem with long running experiments, so it's worth the extra time to engineer them out of the circuit. From what I can see they're only used to power the op-amp. The 'floating ground' trick is s.o.p. when…

I said reference voltage, but I meant the voltage for the summing amp would need to be 9V if that's the step up range he's going for. I totally agree about eliminating the batteries if possible; I just wasn't sure how to get adequate voltage available to the amp without the 9V batteries. But again, it's been many years since I've even looked at a schematic. The floating ground idea looks extremely cool though.

Reading the post again he might be able to completely get rid of the whole circuit by placing two Ge diodes in series with the 0 terminal of the LM35, that will raise the 0 by 0.4 V, just enough to get over the threshold.

Re: Ask HN: What are you working on?

#108

Post by vinutheraj »

samdk wrote: post #25

I'm working on a collaboration tool built to help government agencies and aid organizations coordinate during emergencies. I helped start it this summer as part of the Humanitarian FOSS Project (hfoss.org). It was used successfully in beta for Thanksgiving-day feeding coordination and we're getting very close to our first non-beta release. http://collabbit.org http://github.com/elitheeli/collabbit If you'd like a loo…

Is it something similar to Sahana - http://en.wikipedia.org/wiki/Sahana_FOSS_Disaster_Management... ?

Re: Ask HN: What are you working on?

#109

Post by jacquesm »

jgrahamc wrote: post #102
jacquesm wrote: post #3

Earlier quoted context omitted.

You can possibly get rid of the pair of 9V batteries by using a floating ground that you make with two resistors.

Agreed. I am redesigning it for the production version. I'd like to pull everything from the USB if possible.

Have you tried simply raising the ground of the LM 35 by placing a diode in series with the 0 terminal?

That way you might just add a single 10ct component and get rid of the problem completely.

Just enough to raise the ground of the LM35 above the input sensitivity threshold.

One Si diode would probably work, two Ge in series would be slightly better (because you get more range).

So that would be:

          +
          |
          |
      +---+--+
      | lm35 +---- out
      +---+--+
          |
         ---
         \ /
          v
         ---
          | 
          |
       ---+-- gnd
The diode is 'up side down', you simply use the voltage drop to raise the 0 of the lm35 (like a zener diode), it doesn't know any better and will add the output voltage to the ~0.6 V the diode provides.
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