... 98 ... 99 ... 100..........101! - Here I come!!
Finaly got the last bits togeter in the 8-bit potentiometer I started working with, before examens pressure got too high.
Well, see for your self, the PCB is 20x8.5 cm single sided. There's nothing to it. - Realy! Works as a charm. Stable in the LSB too!
I have changed quite a few things since the last 'version'. For once I changed the 4027 to a 4013 CMOS SR flip-flop. The 'feedback' resistor should be 22M ohms, not 100. I dumped R6 which made the circuit not work.
The board holds it own 5 and 12V PSU, so it can be driven directly from a small transformer. It should be at least 12V or larger. I don't know exactly how many V's before the 7812 gets too hot though.
The last troubble I had was with the transistors driving the relays. The ADC think it's okay to output 1.2 V as digital LOW. I totaly disagree. The BC547C's too! I simply couldn't get a good enough LOW and HI ratio. I got 11.5 V allright as HIGH, but 2.6 V as LOW, this was not good enough to make the relays fall back.
After 2 days of trying different base resistors and drinking way too many coca-cola's, I changed the transistors to 2N5551's with a much lower Hfe. The base resistors is now 66K.
IMPORTANT:
The E and C pins are swapped, so the flat side of the transistor must face the oposite direction as the layout shows. The B pin is still in the middle.
There's the overlay picture for mounting the components:
Finaly got the last bits togeter in the 8-bit potentiometer I started working with, before examens pressure got too high.
Well, see for your self, the PCB is 20x8.5 cm single sided. There's nothing to it. - Realy! Works as a charm. Stable in the LSB too!
I have changed quite a few things since the last 'version'. For once I changed the 4027 to a 4013 CMOS SR flip-flop. The 'feedback' resistor should be 22M ohms, not 100. I dumped R6 which made the circuit not work.
The board holds it own 5 and 12V PSU, so it can be driven directly from a small transformer. It should be at least 12V or larger. I don't know exactly how many V's before the 7812 gets too hot though.
The last troubble I had was with the transistors driving the relays. The ADC think it's okay to output 1.2 V as digital LOW. I totaly disagree. The BC547C's too! I simply couldn't get a good enough LOW and HI ratio. I got 11.5 V allright as HIGH, but 2.6 V as LOW, this was not good enough to make the relays fall back.
After 2 days of trying different base resistors and drinking way too many coca-cola's, I changed the transistors to 2N5551's with a much lower Hfe. The base resistors is now 66K.
IMPORTANT:
The E and C pins are swapped, so the flat side of the transistor must face the oposite direction as the layout shows. The B pin is still in the middle.
There's the overlay picture for mounting the components:
transistors turning on relays
<em><b>The last troubble I had was with the transistors driving the relays. The ADC think it's okay to output 1.2 V as digital LOW. I totaly disagree. The BC547C's too! I simply couldn't get a good enough LOW and HI ratio. I got 11.5 V allright as HIGH, but 2.6 V as LOW, this was not good enough to make the relays fall back.</em></b><p> that's why a ULN2803a relay driver is such a nice chip -- and it's less expensive than 8 discrete parts.
<em><b>The last troubble I had was with the transistors driving the relays. The ADC think it's okay to output 1.2 V as digital LOW. I totaly disagree. The BC547C's too! I simply couldn't get a good enough LOW and HI ratio. I got 11.5 V allright as HIGH, but 2.6 V as LOW, this was not good enough to make the relays fall back.</em></b><p> that's why a ULN2803a relay driver is such a nice chip -- and it's less expensive than 8 discrete parts.
By the way, I have put up a real 600 dpi PDF file for the film here:
http://members.fortunecity.com/minialeph/digipotfilm_pdf.zip
Guess the first one wasn't too sharp.
http://members.fortunecity.com/minialeph/digipotfilm_pdf.zip
Guess the first one wasn't too sharp.
Final schematic would be really helpful
and could you make pdf overlay to?
like this one
http://www.diyaudio.com/forums/showthread.php?postid=123136#post123136
and could you make pdf overlay to?
like this one
http://www.diyaudio.com/forums/showthread.php?postid=123136#post123136
Mark A. Gulbrandsen said:
There are some switching noise when turning up or down. I guess the original aleph-P got the same 'problem'. I can't see anything in the schematic to prevent this anyhow.
I will post the schematic when I got some time later today. I have to 'clean' it up before posting, as it seems a bit messy at this point.
Two things to say:
1. I can't link direct, so you have to goto http://members.fortunecity.com/minialeph to download the file. - That would be for the 600 dpi PDF film download.
2. We are talking Single Ended here. Sorry for those who think this was balanced, because it's not.
1. I can't link direct, so you have to goto http://members.fortunecity.com/minialeph to download the file. - That would be for the 600 dpi PDF film download.
2. We are talking Single Ended here. Sorry for those who think this was balanced, because it's not.
for Thomas
Hi,
solution is just putting one zener diode (ca 2 to 6V) in series with base resistor. Now, with only 66K 2n5551 is maybe in active region, not in high resistance, when is Vout LOW 1,2V on ADC out. Then current Ic may flow thru relay (not enough to enegize, but flow), and you waste power from PS.
(you have not forbidden region between state on-off switching). Zener may help. (then Rb must be smaler; 10 K or so)
regards
zzeenn
Hi,
solution is just putting one zener diode (ca 2 to 6V) in series with base resistor. Now, with only 66K 2n5551 is maybe in active region, not in high resistance, when is Vout LOW 1,2V on ADC out. Then current Ic may flow thru relay (not enough to enegize, but flow), and you waste power from PS.
(you have not forbidden region between state on-off switching). Zener may help. (then Rb must be smaler; 10 K or so)
regards
zzeenn
xsnailx said:about to make it ballanced it should be no problem as we need to attenaute 2 lines + and - we will have to make 2 of them for ballanced operation- hmm am i right
...And controll them both by a dual gang potentiometer. I guess it could be done. But then, I would make an other board with just the relays and the ladder resistors, possibly relay drivers too. - And then connect them parallel to the first board. Like 'master' and 'slave' boards.
It seems there are some interest in a balanced version too. Should i make one?
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