I'm a postgraduate student at the Indian Institute of Astrophysics, Bangalore, India. I'm working on a 6- chaannel photodiode amplifier, which will be used for site surveys for a new telescope coming up in India.
A dual JFET opamp (LT1464) powered by ±15V supply is used to amplify the signals from a very sensitive photodiode (Thorlabs FDS1010) In the first stage, the current in the range of nanoamperes from the photodiode is converted to desirable volt range by a resistance of 9.1MΩ.
Thereafter, DC and AC components of the signal are separated and given different amplification coefficients with the second stage, along with another low pass filter that eliminates all frequencies above 400 Hz. AC component of the signal is amplified by 110 times, while the DC is amplified by 2 times so as to bring out the scintillations from what would have been a DC dominated signal. A high pass filter is also integrated into the circuit to only admit all frequencies over 0.1 Hz. Necessity of clean power requires appropriate smoothening capacitors, to be connected across the power supply of the amplifier
With the current circuit configuration, the circuit tends to oscillate giving an output sinusoidal signal of less than 15V amplitude, without the application of any signal. According to Fig, it’s giving a sinusoidal signal of about 10-12V with NO DC offset, and a frequency of 564Hz in the absence of light from the LED (or for that matter, any light at all). Even when the photodiode was disconnected, the oscillations were still present, as shown in the figure
Following is the PCB layout
After reading more about PCB design, I found that the PCB was full of parasitic capacitances and there was plenty of crosstalk between the output of the six channels. So I decided to separate all the channels and adopt a better PCB design
I'm making another board after reading through some PCB guidelines. I'm populating it only with SMD Resistors and caps (hopefully reducing the noise) and giving a proper ground and power plane. So, can you tell me whether there's any problem with this design before I give it for fabrication?
Following is the PCB design without the ground plane (for better visibility of the layout)
I have a startup and we have NO CLUE about any of this and we need something that is small, can play video or a photo slideshow without an OS and can attach a screen and need it as thin/compact as possible... How do we go about doing this and cheap or is their something that already exists?
I think you should better displace components, reducing trace lengths and loop areas. For example move 22pF and 15pF more closely to the opamp and change the routing of the connection between 10uF and 200K, avoiding the big loop around J3. Try also with traces mainly in one direction on one pcb side and perpendicular on the other one. In order to reduce parasitic capacitance, you should design pcb avoiding traces running too close on the same side or too close between the two pcb sides. In such critical circuit, pcb must be designed with care in order to avoid big issues.
Hope this help.
i want to design a self generating emf device without using any external voltage source ..
please upload the circuit diagram along with the components name..
i want to know about the future scope of my project.
my project is frequency and pulsewidth measurement using 8051 microcontroller
My project involves displaying time coming in computer clock on lcd by using AT 89c51 microcontroller.
Im not able to program 8951 properly .I need assembly lang program to display clock on LCD .A signal will come from computer DB -9 port to input port of 8051 via RS -232 cable ..
This project is way beyond my competency .So please help me completing this project
PLEASE HELP ASAP
please let me know on my email id : firstname.lastname@example.org
Is there a way to make a professional looking homemade pcb without using any chemicals. I was thinking of using a cnc machine to etch it and use this solder mask film I saw, would this way work?
Hello, PCB expert,
Here is my question, I have a board done, but it is 3 mils thinner than the spec. is it possible I ask the fab house to redo the soldermask and silkscreen to make it thicker? what is your suggestion if I don't want to rebuild the board.
How thick was the pcb meant to be ?
Did the supplier agree the thickness tolerance when you ordered ? (in which case you could get the supplier to start again)
(Generally speaking I don't think that suppliers of prototype boards keep ultra careful control of board thickness - it's not a key issue to most users.)
If the board is too thin can't you pad it yourself ?
Hi, do you service Latin America?
I acquired some copper clad boards at a good price (free). I then realized that these boards need to be prepped before I go through the UV process. I am currently using a positive process with a kit from MG Chemicals, so I assume I would need to use a coating for the positive process.could you advise me as to what chemical to use and where to get it? Also when we reach the point where we need commercial boards, we will be bugging you people... We are about a 40 min. drive from you in Vancouver WA.
I have a basic RS-422 schematic design and require a small batch of prototype PC boards to be fabricated from this design. Is there a design house that can pick up the manufacture of PC boards directly from a schematic? I realize this is a broad question but need a starting point. Management wants to farm this out and get some boards to work with in hand. It seems the emphasis is not on attention to completing PCB design, but on getting someone who is familiar with PC board design tools to examine the schematic and come up with a best case scenario and boards to begin working with.
Thank you for your input.
You can email your schematic and Bill of Material to email@example.com
Sunstone can give you a quote for doing the layout out of the PCB, manufacture of the bare pcb and having it assembled with components by one of the companies they work with such as Screaming Circuits.
Phil Rilinger - Senior Tech Support Engineer - Newark / Element14
I missed seeing their capability to do board layout design. I appreciate your response!
I have a generic question about PCB packing number, I always specify "THERE SHALL BE A MAXIMUM OF 10 PANELS PER PACKAGE" in PCB fab note, which is I copied from somewhere. is it reasonable to make this requirement. where this number come from.
because my vendor didn't follow this requirement, and send me a pack with 50 panels. does it matter how many board are packed in one package.
I am a beginner and I am very interested in PCB boards. I have been researching about what they are and I need some material to read about them. Where can I learn how all of those circuits work. I am willing to learn but I need some solid information.Like a link to a good website would help. Thanks.
I'm a hobbyist and I would like to get some PCBs and maybe later some PCAs done in China. Do you have any channels that a guy doing design out of his basement could use to have say 100 boards made at the kind of prices that blow away the domestic low end vendors?
I have created a board design in Eagle and have been fabricating / assembling them myself as needed, but now require a larger volume, so I am ordering both fabrication and assembly services (which I have never done before). My concerns in doing this with my design are as follows:
- The diodes I am using are not in the software I am using (Eagle version 6.5.0), so I chose one with dimensions that place the through holes correctly, however, it does not get the drill hole size correct. Also, the terminal blocks I am using have a different drill hole size than those I found in Eagle. Both of these components assemble fine with a 55mil drill hole, so when going through the fabrication quote form online, I specified a minimum drill hole of 55 which is larger than the holes would be otherwise. Is this sufficient to get the board fabricated correctly?
- Related to #1; It appears I need to send the parts for assembly. If so, is it OK that I send slightly different parts than those specified by the software? There are three diodes on a board and they're all the same. The terminal blocks fit where they fit based on the number of holes / pins.
- I have text on the board such that when I transfer a laser printout of it to FR-4 for etching, it is oriented correctly without the need to mirror, etc. Is this the correct orientation to use when ordering fabrication?
Any advice to help save me from having to make all these boards will be greatly appreciated.
I am new at creating PCB boards but i am having some trouble with one which i have to remove the images of the parts but still keeping the holes to be able to then print it on the board with out having to worry about the images overlapping the welding circuits. It is for a binary clock and i am using EAGLE CADSOFT.
From what I can gather, you are worried about the silkscreen affecting the drills on this board. It sounds like you want to eliminate the silkscreen altogether. In that case you would deactivate the tNames and tPlace layers from the Cam processor.
I am working with eagle and I am running into a few problems. See I am using eagle light and eagle light is very limited. First of all it doesn't let you change the shape of a PCB, doesn't let you make more than two layers, and has limited parts. I am looking for a new PCB making software and I need it to do the following.
- Be free
- Be opensource
- Have unlimited schematics and layouts
- Let you make the PCB shape
- Have unlimited packages and libraries
Can you please help me because I can't find a good software off the internet?
Unfotunately, there is no Open Source Software that will offer all of the Features that you are requiring. Indeed. all of these features would require that some investment be made in a Licensed Software Option. Since you are already familiar with, and using, EAGLE LIGHT --- I would suggest upgrading to EAGLE PROFESSIONAL for your requirements. Please Review following Links:
Hope this helps.
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