On Saturday 15 March 2014 15:57:25 Philipp Burch did opine: > Hi Gene! > > On 03/14/2014 09:23 PM, Gene Heskett wrote: > > Greetings again; > > > > After putting in a diode, that part seemed to work, but this C41 seems > > to have gone south again. (and again (and again)), and its looking > > like a 4th one has failed. Symptoms seem to be an output impedance > > in the 100k region, making 375 rpm maximum, and dropping nearly 100 > > rpm when I put a 10 megohm digital meter on its output to measure it, > > and getting a hair over 5 volts for my trouble, and a fresh LM358 in > > the output voltage follower stage acts exactly like the one I pulled > > out thinking it was bad. > > > > So it looks like I need another, but it seems to me there ought to be > > another choice besides this non-linear POS, and the PMDX-106. Or, do > > I fire up eagle & design my own? > > > > The PMDX-106 works great, but its physically too big for the area it > > needs to fit in by about an inch both ways. > > > > Anybody else got any suggestions? > > > > Thanks guys. > > Do you talk about this unit? > > http://cnc4pc.com/Tech_Docs/C41R2_USER_MANUAL.pdf
I have the R1 version. > I think it should be fairly easy to reverse-engineer the schematic of > this little thingy, as there are only through-hole components and (as it > looks like) just a single copper layer. I thought I had saved one of the blown ones, which would make it easier to see is my mods to that one were less invasive of pcb real estate, but I can't find it, so I must have binned it last fall. > But your comment about the LM358 in conjunction with the problem that > you cannot go below ~200mV output voltage caught my attention: The > LM358's output stage does not really sink current down to GND, so if the > input of your following circuit does not have a pull down, I don't believe it does, > it is likely > that this amplifier is the cause of the problem. If so, you could simply > replace it by a RRIO (rail-to-rail input and output) type, most standard > opamps are pin compatible. If 16V max. Vcc are enough, the TLV2372 could > be a suitable replacement. There should be many more to suit your needs, > a quick parametric search yields at least three parts which should fit > as well: > > http://www.ti.com/lsds/ti/amplifiers-linear/operational-amplifier-op-amp > -products.page#p78=In;Out&p1261max=32;36V;36&p480=2;2&p10max=0.02;100000 > 0&p2954=PDIP That OPA2241 looks like just the ticket. 3 ea samples ordered. :) > Cheers, > Philipp Thanks for the legwork Philip, your google foo is better than mine as my FF is busted & I had to finish the order with chromium. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/13534_NeoTech _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
