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Old 25-11-2017, 02:37 PM
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luka is offline
Join Date: Apr 2007
Location: Perth, Australia
Posts: 1,126
Guys, Grim posted lots of updates about design improvements to all Cams. You should read it yourself here (start with post 2995) but the main points are here:

1. In the CAM86, this effect is weaker, but it is also recommended to feed the ATMega328 and 74HC86 processor from a separate power regulator. Those. The Ft2232 power supply circuit must be decoupled from the ATMega328 and 74HC86 power circuits.

2. The MAX743 transducer should be better out of the board and even the camera in general. This will save you from a lot of problems with interference and unnecessary noise in the picture. Especially in CAM90.

3. During the accumulation of the signal, instead of +15 volts per sensor and on the amplifier chip, a "supporting" +5 volts supply is supplied. So, this voltage + 5 volts can generally be removed to zero. Those. Connect the anode (+) of the diode to ground instead of +5 volts.
Generally speaking, even the +15 volt supply voltage can always be removed, only when the frame is read, it will be better - the operator and sensor will be warmer less, which will improve cooling and reduce noise. For short exposures <1 sec will need to keep +15 permanently. This will require upgrading the firmware.

4. is necessary to properly connect the power wires supplying the "+" and "-" peltiers to the source of the power switching transistor, otherwise there will be some banding of the image. It is necessary to drive these wires separately from the input connector and it is better to use a separate connector for powering the cooling power section.
In the modernized firmware, the switching is carried out during the pulses of the vertical (V1..V4) sweep.

5. Now on the humidity sensor. I'm becoming increasingly convinced of its uselessness. Its readings are obtained only when the sensor is freely blasted, and it naturally does not exist in the hermetic chamber volume. When the sensor is shown above the dew point, there is still fogging. I think there are local moisture anomalies, cold parts (sensor and finger) accumulate water on themselves, drying the rest of the air in the chamber, which is "dry" and registers the sensor. Everything would be fine if a small fan (hair dryer) is installed in the hermetic chamber space. In the new firmware I just removed it.

6. ...when wiring the earth's feet of the sensor, it is better to pour the polygon through the "thermals" to reduce the loss of cold through the legs.

7. Reduce the hermetic chilled volume. You can do this as follows. When wiring the board, consider the possibility of creating a small sealed volume directly on the board. The walls of this volume will be a round or square cylinder. The side edges are made of plastic, the upper part is a protective glass, the lower part is a plate with a hole for the cold finger. The sensor is located inside this cylinder. The entire volume of this cylinder is filled with dry air. Full tightness is provided. Those. the adapter holes in the board are sealed, the slots between the cover glass, the cold finger, the plate and the plastic walls of the cylinder are sealed with a sealant or a rubber ring.
For thermal insulation and electrical insulation of the cold finger, a washer and nut from the insulator are provided.
The temperature sensor is located directly on the bottom surface of the sensor inside this sealed volume.
To do this, it must be diluted right next to the hole for the cold finger.
This is one of the options.

8. The rest of the chamber is filled with Silicone Sealant Pentelast 710. or other similar. Up to the very cover. Protective glass, naturally not poured
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