I'd like to take a closer look at the X-700's electronics in the coming days.
On the one hand, I would like to understand how the circuit basically works, and on the other hand, I am interested in details that can be seen on the flexible circuit board.
It's always fascinating to me what solutions the Japanese engineers have come up with here
A golden work of art: ASA setting and exposure compensation
Today I will examine how the ASA setting and exposure compensation work.
On the left side of the X-700 there is the rewind crank with ASA setting and exposure compensation dial which can be rotated:
This is what it looks like under the top cover:
A ring with two wipers that are electrically connected to each other rotates on gold-plated contact tracks:
Here you can see the setup parted from the camera.
The arrow points to the two wipers, which run separately on both contact tracks:
The inner contact track is narrower and runs continuously without interruptions (orange arrow).
The outer contact track consists of individual, separate contact segments that are electrically connected to each other via a grey layer of resistance material (blue arrow).
Everything together including the wipers results in a variable resistor:
Variable resistor: changing voltage
A variable resistor allows you to alter the amount of current that flows through the resistor.
This also changes the voltage that drops across the resistor integrated in a circuit, e.g. 2 millivolts or 5 millivolts (2/1000 volt, 5/1000 volt).
And the circuitry of the X-700 can work with voltages.
Here, with the ASA setting and exposure compensation, the X-700 can distinguish between different voltage values.
Because when I turn the adjustment dial on the camera, the position of the wipers on the two contact tracks also changes. And since this is a variable resistor, the voltage values also change.
For example, the 2 millivolts could stand for ASA 100 and the 5 millivolts for ASA 400.
That's my assumption.
Multimeter in action
I wanted to determine whether this could be true by taking a closer look with my multimeter.
With a multimeter you can, among other things, measure the value of resistors. The higher the resistance value, the more ohms are measured.
Here the photo from before again:
I place one measuring tip of the multimeter on the grey resistance layer on the outer contact track and the other measuring tip on the inner contact track (purple circles).
Both contact tracks are connected to each other via the wipers, which act like a electrically conducting bridge (yellow bar).
When I switch on the multimeter, a measuring current flows through the grey resistance layer (+) across the bridge to the inner contact track (-) and back to the multimeter.
The further the bridge is from the measuring tips, the longer the resistance layer that the measuring current has to overcome.
This increases the resistance, less current flows and the voltage increases.
In a nutshell:
When I turn the dial on the X-700, the voltage values change and the camera knows which ASA value or exposure correction is set.
Measuring resistance
Here I measure different resistance values with the multimeter.
As already noted, the further away the two wipers (bridge) are from the measuring tips, the higher the resistance:
10.23 kiloohm (= 10,230 Ohm)
14.71 kiloohm
17.59 kiloohm
Confirmed
Of course, this is only part of the circuit for the ASA and exposure compensation setting.
But I think a very interesting one
By the way, why are the contacts gold plated?
The wafer-thin gold layer ensures perfect electrical contact and is corrosion-resistant.
Here the Minolta engineers played it safe
+++
All information provided without guarantee and use at your own risk.
To be continued
On the one hand, I would like to understand how the circuit basically works, and on the other hand, I am interested in details that can be seen on the flexible circuit board.
It's always fascinating to me what solutions the Japanese engineers have come up with here
A golden work of art: ASA setting and exposure compensation
Today I will examine how the ASA setting and exposure compensation work.
On the left side of the X-700 there is the rewind crank with ASA setting and exposure compensation dial which can be rotated:
This is what it looks like under the top cover:
A ring with two wipers that are electrically connected to each other rotates on gold-plated contact tracks:
Here you can see the setup parted from the camera.
The arrow points to the two wipers, which run separately on both contact tracks:
The inner contact track is narrower and runs continuously without interruptions (orange arrow).
The outer contact track consists of individual, separate contact segments that are electrically connected to each other via a grey layer of resistance material (blue arrow).
Everything together including the wipers results in a variable resistor:
Variable resistor: changing voltage
A variable resistor allows you to alter the amount of current that flows through the resistor.
This also changes the voltage that drops across the resistor integrated in a circuit, e.g. 2 millivolts or 5 millivolts (2/1000 volt, 5/1000 volt).
And the circuitry of the X-700 can work with voltages.
Here, with the ASA setting and exposure compensation, the X-700 can distinguish between different voltage values.
Because when I turn the adjustment dial on the camera, the position of the wipers on the two contact tracks also changes. And since this is a variable resistor, the voltage values also change.
For example, the 2 millivolts could stand for ASA 100 and the 5 millivolts for ASA 400.
That's my assumption.
Multimeter in action
I wanted to determine whether this could be true by taking a closer look with my multimeter.
With a multimeter you can, among other things, measure the value of resistors. The higher the resistance value, the more ohms are measured.
Here the photo from before again:
I place one measuring tip of the multimeter on the grey resistance layer on the outer contact track and the other measuring tip on the inner contact track (purple circles).
Both contact tracks are connected to each other via the wipers, which act like a electrically conducting bridge (yellow bar).
When I switch on the multimeter, a measuring current flows through the grey resistance layer (+) across the bridge to the inner contact track (-) and back to the multimeter.
The further the bridge is from the measuring tips, the longer the resistance layer that the measuring current has to overcome.
This increases the resistance, less current flows and the voltage increases.
In a nutshell:
When I turn the dial on the X-700, the voltage values change and the camera knows which ASA value or exposure correction is set.
Measuring resistance
Here I measure different resistance values with the multimeter.
As already noted, the further away the two wipers (bridge) are from the measuring tips, the higher the resistance:
10.23 kiloohm (= 10,230 Ohm)
14.71 kiloohm
17.59 kiloohm
Confirmed
Of course, this is only part of the circuit for the ASA and exposure compensation setting.
But I think a very interesting one
By the way, why are the contacts gold plated?
The wafer-thin gold layer ensures perfect electrical contact and is corrosion-resistant.
Here the Minolta engineers played it safe
+++
All information provided without guarantee and use at your own risk.
To be continued
Last edited: